Hydropower Electricity Generation, 2 Generator ... as well as with the main synchronization parameters of a synchro-check relay, such as the frequency difference ( ûf), voltage difference

© Festo Didactic 86369-00 53

When you have completed this exercise, you will be able to synchronize a three-phase synchronous generator to a live ac power system (i.e., a live bus) using a synchro-check relay. You will be familiar with the operation of a synchro-check relay as well as with the main synchronization parameters of a synchro-check relay, such as the frequency difference ( f), voltage difference ( V), and phase angle difference ( ). You will know how to connect a three-phase synchronous generator to a dead bus using a synchro-check relay.

The Discussion of this exercise covers the following points:

Generator synchronization using a synchro-check relay

Main synchronization parameters of a synchro-check relay

Frequency difference ( f)

Voltage difference ( E)

Phase angle difference ( )

Synchronization window

Circuit-breaker operate time

Distinction between a live bus, an infinite bus, and a dead bus

Connecting a synchronous generator to a dead bus

Generator synchronization using a synchro-check relay

In the manual Three-Phase Rotating Machines, you saw that the process of connecting generators to an ac power system is called generator synchronization. Before synchronizing (i.e., before connecting) a three-phase synchronous generator to an ac power system, it is important to ensure that the following synchronization conditions are met:

The phase sequence of the synchronous generator must be the same as that of the ac power system.

The synchronous generator output frequency must be equal to the

ac power system frequency .

The synchronous generator voltage must be equal to the ac power

system voltage .

The synchronous generator voltage must be in phase with the ac power system voltage.

You also saw that manual synchronization of a synchronous generator to the ac power system is achieved using synchronizing lamps and a synchroscope. Although this method is acceptable, it requires the constant supervision of qualified personnel to be used effectively. Also, the precision of generator

Generator Synchronization Using a Synchro-Check Relay

Exercise 2

EXERCISE OBJECTIVE

DISCUSSION OUTLINE

DISCUSSION

Exercise 2 – Generator Synchronization Using a Synchro-Check Relay Discussion

54 © Festo Didactic 86369-00

synchronization using the manual method relies on human observations and reactions, which are slow compared to the quickness of operation of electronic control devices. Furthermore, humans are subject to errors which can seriously compromise the precision of the generator synchronization process.

For these reasons, generator synchronization is often achieved automatically using a synchro-check relay. A synchro-check relay is a device that controls the state of the circuit breaker (generally a normally open three-phase contactor) used to connect the synchronous generator to the ac power system, as shown in Figure 29. A synchro-check relay is characterized by a number of synchronization parameters (these are presented later in this discussion), each defining a particular synchronization condition that must be met before the synchro-check relay sends the control signal for the circuit breaker to close. By carefully refining the synchro-check relay parameters, it is thus possible to ensure that generator synchronization occurs only when the frequency, magnitude, and phase angle of the generator voltage are very close to those of the ac power system voltage to which it is to be synchronized. Because of this, using a synchro-check relay for generator synchronization is much more precise than manual synchronization. It minimizes current and power transients at the instant of synchronization, as well as the mechanical stress imposed on the synchronous generator shaft and the hydraulic turbine at the instant of synchronization.

Figure 29. Automatic synchronization of a synchronous generator to an ac power system using a synchro-check relay.

Synchro-check relay

Synchro-check relaycontrol signal

Synchronous generator

Circuit breaker

To neutral terminal of the synchronous

generator

N

Generator voltage sensor

AC power system voltage sensor

AC power system



Figure 29 shows that a synchro-check relay measures the line voltage at the synchronous generator side of the circuit breaker and the line voltage at the ac power system side of the circuit breaker. Using the measured generator voltage and ac power system voltage, the synchro-check relay determines if all generator synchronization conditions (i.e., the conditions defined by the synchronization parameters in the synchro-check relay) are met. When all synchronization conditions are met, the synchro-check relay sends a control signal for the circuit breaker to close, thereby allowing generator synchronization to the ac power system. As long as any one of the synchronization conditions is not met, the synchro-check relay sends no control signal to the circuit breaker, thereby preventing generator synchronization to the ac power system.

Figure 30. With a total installed capacity of 6300 MW, the Longtan dam hydropower plant is among the largest in China.

Main synchronization parameters of a synchro-check relay

Synchro-check relays are characterized by a wide variety of synchronization parameters. The required adjustment of the different synchronization parameters of a synchro-check relay in order to ensure that certain synchronization conditions are met before generator synchronization is allowed is a design criterion which depends on the particular requirements of the synchronous generator as well as on those of the ac power system to which it is to be connected.

The three main synchronization parameters of a synchro-check relay are the frequency difference ( f), voltage difference ( E), and phase angle difference ( ). Each parameter represents a synchronization condition that must be met before generator synchronization to the ac power system is allowed. Each parameter is described in detail in the following subsections.



Frequency difference ( f)

The frequency difference or f parameter (expressed in Hz) determines the maximal frequency difference (positive or negative) between the synchronous generator and the ac power system for which generator synchronization is allowed. When the frequency difference between the generator and the ac power system is lower than the f parameter, the f synchronization condition is met. To ensure that the generator frequency is close enough to the ac power system frequency before synchronization, the f synchronization parameter is usually set to a relatively low value (0.5 Hz or less).

Voltage difference ( E)

The voltage difference or E parameter (expressed in % of the ac power system nominal voltage) determines the maximal voltage difference (positive or negative) between the synchronous generator and the ac power system for which generator synchronization is allowed. When the voltage difference between the generator and the ac power system is lower than the E parameter, the E synchronization condition is met. Since the voltage of most ac power systems is rarely exactly at the nominal value, especially during peak hours of energy consumption, the E synchronization parameter is generally not set to a value as restrictive as that of the f parameter, and is usually set to about 5% of the nominal voltage.

Phase angle difference ( )

The phase angle difference or parameter (expressed in degrees) determines the maximal phase angle difference (positive or negative) between the synchronous generator voltage and the ac power system voltage for which generator synchronization is allowed. When the phase angle difference between the generator voltage and the ac power system voltage is equal to or lower than the parameter, the synchronization condition is met. To minimize current and power transients, as well as the mechanical stress on the generator shaft and the hydraulic turbine, the synchronization parameter is usually set to a relatively low value (commonly 20° or less).



Figure 31. View of the Hoover Dam, at the border between the states of Arizona and Nevada, USA. At the end of its construction in 1936, the Hoover Dam was the world’s largest dam hydropower plant. It currently has a total installed capacity of 2080 MW.

Synchronization window

The time window during which all synchronization conditions defined by the synchronization parameters in the synchro-check relay are met is generally designated as the synchronization window. Due to the cyclic nature of generator and ac power system voltage waveforms, this time window repeats at regular intervals when the synchronous generator is close to synchronization. Permissive synchronization conditions tend to increase the duration of the synchronization window and, consequently, allow generator synchronization to occur rapidly. However, when synchronization occurs, the synchronous generator voltage parameters (frequency, magnitude, and phase angle) may be significantly different from those of the ac power system voltage and thus decrease the precision of the synchronization. On the other hand, restrictive synchronization conditions tend to decrease the duration of the synchronization



window and, consequently, delay generator synchronization. However, when synchronization occurs, the synchronous generator voltage parameters are closer to those of the ac power system voltage and thus increase the precision of the synchronization.

Circuit-breaker operate time

The circuit-breaker operate time is an important factor to be taken into account in generator synchronization using a synchro-check relay. The circuit-breaker operate time is the actual time needed for the circuit breaker used for generator synchronization to close after it receives the control signal from the synchro-check relay. The circuit-breaker operate time affects the accuracy of generator synchronization since it delays the instant at which generator synchronization actually occurs. The circuit-breaker operate time becomes highly problematic when it exceeds the duration of the synchronization window since this causes generator synchronization to happen when the synchronization conditions (e.g., the f, E, and parameters) are no longer met (i.e., after the synchronization window has elapsed).

To prevent generator synchronization from occurring after the synchronization window, an additional parameter, referred to as the circuit-breaker operate time, is available in most synchro-check relays. The value of the circuit-breaker operate time parameter is set to be close to the actual operate time of the circuit breaker used for generator synchronization. The circuit-breaker operate time parameter adds a final condition before the synchro-check relay allows generator synchronization. When the synchro-check relay determines that all synchronization conditions defined by the other synchronization parameters are met, it verifies whether or not the value of the circuit-breaker operate time parameter is shorter than the synchronization window (i.e., that the circuit breaker would close before the synchronization window elapses). When this condition is met, the synchro-check relay allows generator synchronization. This is illustrated in Figure 32a. On the other hand, when the value of the circuit-breaker operate time parameter is longer than the synchronization window (i.e., when the circuit breaker would close after the synchronization window elapses), the condition is not met and the synchro-check relay prevents generator synchronization. This is illustrated in Figure 32b.



Figure 32. Effect of the circuit-breaker operate time parameter on synchro-check relay operation.

Note that the value of the circuit-breaker operate time parameter of the synchro-check relay is not necessarily made equal to the actual circuit-breaker operate time. In fact, the value of the circuit-breaker operate time parameter is often made slightly longer than the actual circuit-breaker operate time to ensure that the resulting delay in generator synchronization is shorter than the length of the synchronization window. Consequently, this ensures that generator synchronization effectively occurs before the end of the synchronization window.

Distinction between a live bus, an infinite bus, and a dead bus

Thus far, we have assumed that the ac power system to which a synchronous generator is synchronized is both infinite and live.

A live bus is one that is powered by an ac power system whose voltage is high enough to be considered live. The value of the minimal voltage required for a bus to be considered live is called the live bus voltage threshold. It is a parameter implemented in most synchro-check relays. Its value is a design criterion which depends on the nature and the uses of the bus.

An infinite bus is one that is powered by an ac power system so powerful that it imposes the magnitude, frequency, and phase angle of the voltage to any device connected to the bus, no matter the loading condition of the ac power system. For example, when a synchronous generator is connected to an infinite bus, it immediately begins operating at the same voltage, frequency, and phase angle as the ac power system. This means that, in an infinite bus, all synchronous generators operate in perfect synchronism (i.e., at the same speed, frequency, and phase angle) and at the same voltage. By definition, an infinite bus is also a

Circuit-breaker operate time parameter

Circuit-breaker operate time parameter

The circuit breaker receives thecontrol signal to close from the

synchro-check relay

(b) The synchro-check relay prevents generator synchronization because the circuit-breaker operate time parameter is longer than the duration of the synchronization window.

(a) The synchro-check relay allows generator synchronization because the circuit-breaker operate time parameter is shorter than the duration of the synchronization window.

Duration of the synchronization window

Duration of the synchronization window

The circuit breaker receives nocontrol signal to close from the

synchro-check relay



live bus (unless the bus is temporarily shut down, such as during a power outage). Most large ac power networks are considered infinite buses.

In most cases, synchronous generators are connected to an infinite bus such as the ac power network to adjust the amount of power available in the network to the electric power demand. However, it is also common to connect synchronous generators to a dead bus. A dead bus is one that is powered by an ac power system whose voltage is low enough to be considered dead. The value of the maximal voltage under which a bus is considered dead is called the dead bus voltage threshold. It is a parameter implemented in most synchro-check relays. Just as for the live bus voltage threshold, the value of the dead bus voltage threshold is a design criterion which depends on the nature and the uses of the bus. Common examples of dead buses include isolated loads (e.g., electric power consumers on an island) and blacked-out power networks.

Figure 33. Satellite view of the Tucuruí dam hydropower plant in Brazil. With an installed capacity of 8370 MW, it is one of the largest hydropower plants in the world, and the first large-scale hydroelectrical project in the Brazilian Amazon rainforest.



Connecting a synchronous generator to a dead bus

Although synchronous generators are usually synchronized (i.e., connected) to a live bus, it is sometimes necessary to connect a synchronous generator to a dead bus. Due to the differences between a live bus and a dead bus, connecting a synchronous generator to a dead bus has very different requirements than synchronizing a synchronous generator to a live bus. Another possibility is that the synchronous generator itself is dead (i.e., the synchronous generator voltage is equal to or lower than the dead bus voltage threshold parameter), making it useless to connect the synchronous generator to the bus. It is therefore imperative that a synchro-check relay verifies the condition of both the synchronous generator and the bus (i.e., the ac power system powering the bus) to which it is to be connected before allowing connection of the generator to this bus.

To achieve this, before attempting to synchronize a synchronous generator to an ac power bus, the synchro-check relay first measures the generator voltage and the bus voltage, then compares these measured values to the live bus voltage threshold parameter (referred to as ) and the dead bus voltage threshold

parameter (referred to as ). When the generator voltage is equal to or higher than the live bus voltage threshold, the generator is considered live. In this case, one of the following conditions is possible:

Live generator and live bus condition: When the measured bus voltage is higher than the dead bus voltage threshold, the bus is considered live. The synchro-check relay begins the procedure for synchronizing a synchronous generator to a live bus, as described in the previous sections of this exercise. In this case, generator synchronization to the ac power system powering the bus will occur when all synchronization conditions are met.

Live generator and dead bus condition: When the measured bus voltage is lower than the dead bus voltage threshold, the synchro-check relay waits for a length of time equal to the dead time parameter. After that, if the initial conditions observed persist, the bus is considered dead. The synchronous generator is immediately connected to the dead bus to supply ac power to the load connected to the bus. The voltage, frequency, and phase angle measured at the bus immediately become equal to those of the synchronous generator.

When the measured generator voltage is not higher than the live bus voltage threshold, the generator is considered to be dead. In this case, the synchro-check relay prevents connection of the synchronous generator to the bus and continues to measure the generator voltage and bus voltage until one of the above conditions is observed (i.e., until the generator is considered to be live and the bus is determined to be either live or dead).

The dead time parameter

corresponds to the length of

time during which the dead

bus condition must persist

in order for the bus tested to

be considered dead. The

dead time parameter en-

sures that the dead bus

condition is permanent and

not simply due to a voltage

transient.

Exercise 2 – Generator Synchronization Using a Synchro-Check Relay Procedure Outline


Figure 34. The Krasnoyarsk dam is one of the largest hydropower plants in Russia, with an installed capacity of 6000 MW. In the figure, one of the dam spillways is open, allowing water to flow from the reservoir directly into the water output (photo courtesy of Alex Polezhaev).

The Procedure is divided into the following sections:

Set up and connections

Synchro-check relay operation (connection to a dead bus)

Synchro-check relay operation (synchronization to a live bus)

Effects of the synchro-check relay parameter settings on the electrical transients and mechanical stress at generator synchronization

Active and reactive power control of a turbine-driven generator after connection to a live infinite bus

High voltages are present in this laboratory exercise. Do not make or modify any

banana jack connections with the power on unless otherwise specified.

Set up and connections

In this section, you will set up a synchronous generator driven by a hydraulic turbine and connected to both a three-phase resistive load and the ac power network through a three-phase contactor. You will then set up the synchro-check relay for connection of the synchronous generator to a dead bus.

PROCEDURE OUTLINE

PROCEDURE

Exercise 2 – Generator Synchronization Using a Synchro-Check Relay Procedure


1. Refer to the Equipment Utilization Chart in Appendix A to obtain the list of equipment required to perform this exercise.

Install the required equipment in the Workstation.

Before coupling rotating machines, make absolutely sure that power is turned off

to prevent any machine from starting inadvertently.

Mechanically couple the Synchronous Motor/Generator to the Four-Quadrant Dynamometer/Power Supply using a timing belt.

2. Make sure the ac and dc power switches on the Power Supply are set to the O (off) position, then connect the Power Supply to a three-phase ac power outlet.

Make sure the main power switch on the Four-Quadrant Dynamometer/Power Supply is set to the O (off) position, then connect its Power Input to an ac power outlet.

Connect the Power Input of the Data Acquisition and Control Interface to a 24 V ac power supply.

Connect the Low Power Input of the Power Thyristors module to the Power Input of the Data Acquisition and Control Interface. Turn the 24 V ac power supply on.

3. Connect the USB port of the Data Acquisition and Control Interface to a USB port of the host computer.

Connect the USB port of the Four-Quadrant Dynamometer/Power Supply to a USB port of the host computer.

4. Turn the Four-Quadrant Dynamometer/Power Supply on, then set the Operating Mode switch to Dynamometer.

5. Turn the host computer on, then start the LVDAC-EMS software.

In the LVDAC-EMS Start-Up window, make sure the Data Acquisition and Control Interface and the Four-Quadrant Dynamometer/Power Supply are detected. Make sure the Computer-Based Instrumentation and Synchronous Generator Control functions are available for the Data Acquisition and Control Interface module. Make sure that the Turbine Emulator function is available for the Four-Quadrant Dynamometer/Power Supply. Also, select the network voltage and frequency that correspond to the voltage and frequency of the local ac power network, then click the OK button to close the LVDAC-EMS Start-Up window.



6. Connect the equipment as shown in Figure 35. Use the Four-Quadrant Dynamometer/Power Supply and the Power Supply to implement the hydraulic-turbine emulator and three-phase ac power source, respectively. Also, use the Power Thyristors module to implement the thyristor three-phase bridge. In this circuit, the three-phase ac power source supplies power to the thyristor three-phase bridge and the bus to which the three-phase resistive load is connected.

When connecting the thyristor three-phase bridge, make sure switches S1

and S2 on the Power Thyristors module are set to the I (closed) position. Doing so connects thyristors Q1 to Q6 in a three-phase bridge configuration.

a In the circuit of Figure 35, inputs E2, E3, E4, I3, and I4 are used to measure the circuit parameters necessary for controlling the synchronous generator when it is connected to a dead bus. Because of this, inputs E2, E3, E4, I3, and I4 cannot be used for circuit parameter measurement and observation in this exercise.



Local ac power network , , ( ) Voltage

(V) Frequency

(Hz)

120 60 1200

220 50 4400

240 50 4800

220 60 4400

Figure 35. Turbine-driven synchronous generator connected to the local ac power network and a three-phase resistive load through a three-phase contactor.

7. On the Resistive Load, make the necessary switch settings to obtain the required resistance value.

8. Make sure the Sync. switch on the Synchronizing Module/Three-Phase Contactor is set to the O position. This allows remote control of the three-phase contactor by the Data Acquisition and Control Interface module.


Hydraulic-turbine

emulator

L1

L2

L3

Three-phase contactor

Thyristor three-phase bridge

Resistive load

L1

L2

L3

N

To neutral terminal of the synchronous generator

Control signal from DACI

Firing signals from DACI



9. Connect the Digital Outputs of the Data Acquisition and Control Interface to the Firing Control Inputs of the Power Thyristors module using the provided cable with DB9 connectors.

10. Connect Digital Output 1 (DO1) of the Data Acquisition and Control Interface to the positive (+) terminal of the Remote Control input on the Synchronizing Module/Three-Phase Contactor using a miniature banana plug lead. Connect a digital (D) common (white terminal) of the Data Acquisition and Control Interface to the negative (-) terminal of the Remote Control input on the Synchronizing Module/Three-Phase Contactor using a miniature banana plug lead.

Connect Analog Output 1 (AO1) of the Data Acquisition and Control Interface to the left-hand side terminal of the Command Input of the Four-Quadrant Dynamometer/Power Supply using a miniature banana plug lead. Connect an analog (A) common (white terminal) of the Data Acquisition and Control Interface to the common (white terminal) of the Command Input on the Four-Quadrant Dynamometer/Power Supply using a miniature banana plug lead.

Connect the A Shaft Encoder Output of the Four-Quadrant Dynamometer/Power Supply to the A Encoder Digital Input of the Data Acquisition and Control Interface using a miniature banana plug lead. Connect the B Shaft Encoder Output of the Four-Quadrant Dynamometer/Power Supply to the B Shaft Encoder Digital Input of the Data Acquisition and Control Interface using a miniature banana plug lead. Connect the common terminal (white) of the Shaft Encoder Outputs on the Four-Quadrant Dynamometer/Power Supply to a digital (D) common (white terminal) of the Encoder Digital Inputs on the Data Acquisition and Control Interface using a miniature banana plug lead.

11. In LVDAC-EMS, open the Synchronous Generator Control window, then make the following settings:

Make sure the Function parameter is set to Hydropower Generator (Dead Bus – Balanced Load). This function allows control of a turbine-driven generator connected to a dead bus. The function includes a synchro-check relay used to control the connection of the generator to the dead bus.

Make sure the Nominal Voltage parameter is set to the nominal value of the local ac power network voltage. This determines the voltage at which the synchro-check relay considers the generator as synchronized to the system.

Make sure the Hydropower Generator (Dead Bus – Balanced Load) function is stopped (i.e., make sure the Status parameter is set to Stopped).



Synchro-Check Relay

Make sure the Live Bus Voltage Threshold parameter is set to 90% of the ac power network nominal voltage . This sets the voltage at which the generator is considered to be live to 90% of the ac power network nominal voltage .

Set the Relay Output parameter to Low. This sets the control voltage at the output of the Synchro-Check Relay (i.e., Digital Output 1 of the Data Acquisition and Control Interface) to 0 V. This forces the three-phase contactor contacts to remain open, which means that they cannot be closed through the synchronization process.

Make sure the Dead Bus Voltage Threshold parameter is set

to 10% of the local ac power network voltage . This sets the voltage below which the bus (i.e., the bus to which the generator is to be connected) is considered to be dead to 10% of the ac power network nominal voltage .

Set the Dead Time parameter to 3 s. This sets to 3 seconds the minimal time during which the live generator and dead bus condition must persist before the synchro-check relay considers the synchronous generator as ready to be connected to the dead bus.

Speed Governor

Set the Generator Speed Command parameter to 50% of the nominal synchronous speed of the synchronous generator.

a The nominal synchronous speed of the Synchronous Motor/Generator is 1500 r/min at a local ac power network frequency of 50 Hz and 1800 r/min at a local ac power network frequency of 60 Hz.

Make sure the Speed Droop parameter is set to 0%. The purpose of this parameter is explained later in the manual.

Make sure the Generator Acceleration parameter is set to 30 r/min / s. This sets the rate at which the speed governor increases or decreases the generator speed to 30 r/min / s.

Automatic Voltage Regulator

Make sure the Thyristor Bridge Firing Control Mode parameter is set to Automatic. This control mode allows the automatic voltage regulator (AVR) to automatically control the generator voltage by varying the generator field current through the firing angle of the thyristor bridge.

Set the Generator Voltage Command parameter to 50% of the local ac power network line voltage.

Make sure the Voltage Droop parameter is set to 0%. The purpose of this parameter is explained later in the manual.



Make sure the Minimum Firing Angle Limit parameter is set to 40°.

Make sure the Maximum Firing Angle Limit parameter is set to 120°.

Make sure that the Proportional Gain [Kp] parameter is set to the value indicated in the following table that corresponds to your local ac power network voltage and frequency.

Table 4. Proportional gain Kp of the automatic voltage regulator of the hydropower generator.

Local ac power network Proportional gain

Kp Voltage (V)

Frequency (Hz)

120 60 5

220 50 2

240 50 1.25

220 60 2

Make sure that the Integral Gain [Ki] parameter is set to the value indicated in the following table that corresponds to your local ac power network voltage and frequency.

Table 5. Integral gain Ki of the automatic voltage regulator of the hydropower generator.

Local ac power network

Integral gain Ki Voltage

(V) Frequency

(Hz)

120 60 20

220 50 10

240 50 5

220 60 10

a Using the speed governor and automatic voltage regulator of the synchronous generator to automatically control the generator speed and voltage enables the synchronization parameters of the synchro-check relay to be studied more easily and accurately. The principles behind the operation of the speed governor and automatic voltage regulator of the synchronous generator are covered in detail in Exercise 3.

12. In LVDAC-EMS, open the Four-Quadrant Dynamometer/Power Supply window, then make the following settings:

Set the Function parameter to Hydraulic-Turbine Emulator.

Set the Vane Control parameter to 8960 Command Input. This setting allows the vane opening of the hydraulic-turbine emulator to be controlled via a signal injected at the Command Input of the Four-Quadrant Dynamometer/Power Supply.



Make sure the Turbine Type parameter is set to 300 W, Francis. This makes the hydraulic-turbine emulator operate as a 300 W Francis turbine.

Make sure the Vane Maximal Speed parameter is set to 10.0%/s. This sets the maximal speed at which the vane of the hydraulic-turbine emulator can open or close to 10%/s.

Make sure the Runner Inertia parameter is set to 0.3 kg·m2. This sets

the runner inertia of the hydraulic-turbine emulator to 0.3 kgám2. The

higher the runner inertia of the hydraulic-turbine emulator, the slower the runner speed increases as water flow increases, and the slower the runner speed decreases as water flow decreases.

Make sure the Hydraulic-Turbine Emulator function is set to Stopped.

13. In LVDAC-EMS, open the Metering window. Make the required settings in order to measure the rms value (ac) of the bus voltage and the bus

frequency (both are measured via input E1).

14. On the Synchronous Motor/Generator, set the Exciter switch to the closed position (I), then turn the Exciter knob fully clockwise (i.e., set it to the Max. position).

Synchro-check relay operation (connection to a dead bus)

In this section, you will first make sure the conditions necessary for connecting the synchronous generator to a dead bus are not met. You will then make the required settings to successively meet all conditions necessary for connecting the synchronous generator to the dead bus, ensuring for each condition that the corresponding status indicator on the synchro-check relay lights up. While doing so, you will observe the effect of each synchronization parameter on the synchro-check relay operation (i.e., the connection of the generator to the dead bus).

15. On the Power Supply, turn the three-phase ac power source on.

In the Four-Quadrant Dynamometer/Power Supply window, start the hydraulic-turbine emulator by clicking the Start/Stop button or by setting the Status parameter to Started.

In the Synchronous Generator Control window, start the hydropower generator by clicking the Start/Stop button or by setting the Status parameter to Started.



16. Wait for the synchronous generator speed and voltage to stabilize. Are

the , , and Synchro-Check Relay Status Indicators in the Synchronous Generator Control window off, indicating that the conditions required for connecting the generator to a dead bus are not met? Briefly explain why for each parameter. Use the values indicated by the meters in the Generator Control and Metering windows to answer this question.

17. On the Power Supply, turn the three-phase ac power source off. While doing so, observe the Synchro-Check Relay Status Indicators in the Synchronous Generator Control window, as well as the meters in the Metering window. What happens as you turn off the ac power source? Explain briefly.

18. In the circuit of Figure 35, remove the three line conductors (L1, L2, and L3) connecting the three-phase ac power source to the three-phase resistive load. This ensures that the three-phase ac power source only supplies power to the thyristor three-phase bridge, and no power to the three-phase resistive load, thereby reproducing a dead bus situation.

On the Power Supply, turn the three-phase ac power source on.



19. In the Synchronous Generator Control window, set the Generator Speed Command parameter to the nominal synchronous speed of the synchronous generator.

In the Synchronous Generator Control window, set the Generator Voltage

Command parameter to the nominal voltage (i.e., the voltage of the local ac power network). While doing so, observe the Synchro-Check Relay Status Indicators and generator voltage in the Synchronous Generator Control window. What happens as the synchronous generator voltage increases to its nominal value? Wait about 10 seconds before answering this question. Explain briefly.

20. In the Synchronous Generator Control window, set the Generator Voltage Command parameter to 50% of the local ac power network line voltage. Then, set the Relay Output parameter to Normal. This causes the synchro-check relay to operate normally (i.e., it lets the synchro-check relay control when to close the contacts of the three-phase contactor). Therefore, the synchro-check relay allows generator connection to the bus when all conditions are met, and prevents generator connection as long as they are not.

In the Synchronous Generator Control window, set the Generator Voltage

Command parameter once again to the nominal voltage (i.e., the voltage of the local ac power network). What happens as the synchronous

generator voltage increases to its nominal value and the Relay Output parameter is set to Normal? Explain briefly.



21. In the Synchronous Generator Control window, set the Relay Output parameter to Low (this opens the three-phase contactor contacts and disconnects the generator from the resistive load), then set the Generator Speed Command and Generator Voltage Command parameters to 0. Wait for the generator to stop rotating, then stop the hydropower generator by clicking the Start/Stop button or by setting the Status parameter to Stopped.

In the Four-Quadrant Dynamometer/Power Supply window, stop the hydraulic-turbine emulator by clicking the Start/Stop button or by setting the Status parameter to Stopped.

On the Power Supply, turn the three-phase ac power source off.

Synchro-check relay operation (synchronization to a live bus)

In this section, you will modify the circuit connections and set the synchro-check relay for synchronization of the synchronous generator to a live bus. You will first make sure the conditions necessary for synchronizing the synchronous generator to a live bus are not met. You will then make the required settings to successively meet all conditions necessary for synchronizing the synchronous generator to a live bus, ensuring for each condition that the corresponding status indicators on the synchro-check relay lights up. While doing so, you will observe the effect of each synchronization parameter on the synchro-check relay operation (i.e., on the generator synchronization).

22. Modify the equipment connections to obtain the circuit shown in Figure 36. Note that, in the circuit, the three-phase resistive load is removed. Also, the high range (40 A) of current input I2 on the Data Acquisition and Control Interface is used to measure one of the stator currents of the synchronous generator. Finally, voltage input E3 changes position in the circuit to measure the generator voltage instead of the ac power network voltage.

a In the circuit of Figure 36, inputs E3, E4, I3, and I4 are used to measure the circuit parameters necessary for controlling the synchronous generator when it is connected to a live infinite bus. Because of this, inputs E3, E4, I3, and I4 cannot be used for circuit parameter measurement and observation in this exercise.



Figure 36. Turbine-driven synchronous generator connected to the local ac power network (live bus) through a three-phase contactor.

23. In LVDAC-EMS, set the Range setting of current input I2 to High.

24. On the Data Acquisition and Control Interface, connect Digital Output 2 (DO2) to Analog Input 1 (AI1) using a miniature banana plug lead. Also connect a digital (D) common (white terminal) to an analog (A) common (white terminal) using a miniature banana plug lead. Digital Output 2 (DO2) provides a TTL signal that can be used to observe the synchronization window when synchronizing the synchronous generator to a

live bus. When the synchronization conditions related to the , f, E, and parameters of the Synchro-Check Relay are all met, the signal at Digital Output 2 passes from 0 V to about 5 V. This indicates that the generator can be synchronized to the live bus provided that the above synchronization conditions are met for a duration exceeding the value of

parameter of the Synchro-Check Relay. The signal at Digital Output 2 returns to 0 V as soon as one of the synchronization conditions related to

the , f, E, and parameters is no longer met. The signal at Digital Output 2 of the Data Acquisition and Control Interface is referred to as the synchronization window signal.


Hydraulic-turbine

emulator

L1

L2

L3

Three-phase contactor

Thyristor three-phase bridge

L1

L2

L3

40 A terminal

N

To neutral terminal of the synchronous generator

Control signal from DACI

Firing signals from DACI



25. In the Synchronous Generator Control window, make the following settings:

Set the Function parameter to Hydropower Generator (Balanced Infinite Bus). This function allows control of a turbine-driven generator connected to a live infinite bus (i.e., the bus powered by the three-phase ac power source in the circuit of Figure 36). The function includes a synchro-check relay to supervise the synchronization of the generator to the live infinite bus.

a The Hydropower Generator (Balanced Infinite Bus) function measures the generator three-phase active power and reactive power using only one voltage input (E3) and one current input (I4). Because of this, the Hydropower Generator (Balanced Infinite Bus) function provides accurate power control of a synchronous generator only when the generator is connected to a balanced infinite bus.

Make sure the Nominal Voltage parameter is set to the nominal value of the local ac power network voltage.

Make sure the Hydropower Generator (Balanced Infinite Bus) function is set to Stopped.

Synchro-Check Relay

Set the Live Bus Voltage Threshold parameter to 80% of the

ac power network nominal voltage

Set the Voltage Difference E parameter to 10% of the ac power network nominal voltage. This sets the maximal difference between the generator voltage and ac power network voltage (i.e., the infinite bus voltage) for which generator synchronization is allowed (provided that all other synchronization conditions are met) to plus or minus 10% of the local ac power network nominal voltage.

Set the Frequency Difference f parameter to 1 Hz. This sets the maximal difference between the generator frequency and ac power network frequency (i.e., the infinite bus frequency) for which generator synchronization is allowed (provided that all other synchronization conditions are met) to plus or minus 1 Hz.

Set the Phase Difference parameter to 45°. This sets the maximal phase angle difference between the generator voltage and ac power network voltage (i.e., the infinite bus voltage) for which generator synchronization is allowed (provided that all other synchronization conditions are met) to plus or minus 45°.

Set the Circuit-Breaker Operate Time parameter to 0.25 s. This sets the minimal duration of the synchronization window for which generator synchronization is allowed (provided that all other synchronization conditions are met) to 0.25 s.



Speed Governor

Set the Generator Speed Command parameter to 80% of the nominal synchronous speed of the synchronous generator.

Make sure the Speed Droop parameter is set to 5%.


Make sure the Thyristor Bridge Firing Control Mode parameter is set to Automatic.

Set the Generator Voltage Command parameter to 70% of the local ac power network line voltage.

Make sure the Voltage Droop parameter to 5%.

Make sure that the Proportional Gain [Kp] parameter is set to the value indicated in the following table that corresponds to your local ac power network voltage and frequency.

Table 6. Proportional gain Kp of the automatic voltage regulator of the hydropower generator.

Local ac power network Proportional gain

Kp Voltage (V)

Frequency (Hz)

120 60 5

220 50 2

240 50 1.25

220 60 1.5

Make sure that the Integral Gain [Ki] parameter is set to the value indicated in the following table that corresponds to your local ac power network voltage and frequency.

Table 7. Integral gain Ki of the automatic voltage regulator of the hydropower generator.

Local ac power network

Integral gain Ki Voltage

(V) Frequency

(Hz)

120 60 20

220 50 10

240 50 5

220 60 8






27. Wait for the synchronous generator speed and voltage to stabilize. Are all Synchro-Check Relay Status Indicators in the Synchronous Generator Control window off? What does it indicate?

28. In the Synchronous Generator Control window, set the Generator Speed Command parameter to 2 r/min below the nominal synchronous speed of the synchronous generator. Wait for the generator speed and voltage to stabilize.

Which of the Synchro-Check Relay Status Indicators in the Synchronous Generator Control window light up permanently? What does it indicate?

29. In the Synchronous Generator Control window, set the Generator Voltage Command parameter to 84% of the local ac power network nominal voltage. Wait for the generator speed and voltage to stabilize.


30. In the Synchronous Generator Control window, set the Generator Voltage Command parameter to the current value of the infinite bus

voltage (indicated in the Metering window). Wait for the generator speed and voltage to stabilize.




31. In LVDAC-EMS, open the Oscilloscope, then make the appropriate settings in order to observe the waveforms of the synchronous generator voltage (input E2) and the infinite bus voltage (input E1). Also, make the appropriate settings to observe the waveform of the synchronization window signal of the Synchro-Check Relay (available at Analog Input 1 of the Data Acquisition and Control Interface).

Describe the waveforms you observe on the Oscilloscope screen.

32. In LVDAC-EMS, open the Phasor Analyzer. Make the required settings in

order to observe the phasors of the generator voltage and the infinite bus voltage . Set the phasor of the infinite bus voltage as the reference phasor.

Observe the phasors of the generator voltage and the infinite bus

voltage as well as the synchronization window signal displayed on the Oscilloscope. Describe what you observe.

33. In the Synchronous Generator Control window, observe the indicator. While doing so, also observe the waveforms and voltage phasors displayed on the Oscilloscope and Phasor Analyzer, respectively. Describe and explain your observations.

34. In the Synchronous Generator Control window, set the Generator Speed Command parameter to 5 r/min below the nominal synchronous speed of the synchronous generator. Wait for the synchronous generator speed and voltage to stabilize.



35. In the Synchronous Generator Control window, observe the and indicators. Notice that whenever the indicator lights up momentarily,

the indicator also lights up momentarily shortly after. Explain why and what it means.

36. In the Synchronous Generator Control window, decrease the Phase Difference parameter to 20°. While doing so, observe the

and indicators in the Synchronous Generator Control window, as well as the synchronization window signal displayed on the Oscilloscope screen.

What happens to the duration of the synchronization window when the Phase Difference parameter is decreased? Explain briefly.

Does the indicator in the Synchronous Generator Control window still lights up momentarily shortly after the indicator lights up, indicating that the duration of the synchronization window is still longer than the circuit-

breaker operate time ( ) parameter?

Yes No

37. In the Synchronous Generator Control window, decrease the Phase Difference parameter to 5° by steps of 5°. While doing so, observe the and indicators in the Synchronous Generator Control window.

Describe what happens as you decrease the Phase Difference parameter to 5°? Explain briefly.

38. In the Synchronous Generator Control window, increase the Phase Difference parameter back to 45°.



39. In the Synchronous Generator Control window, set the Generator Speed Command parameter to 40 r/min below the nominal synchronous speed of the synchronous generator. Wait for the synchronous generator speed and voltage to stabilize, then observe on the Oscilloscope the waveforms of the

synchronous generator voltage and the bus voltage , as well as the synchronization window signal. Also observe the Synchro-Check Relay Status Indicators in the Synchronous Generator Control window.

Describe what you observe as the generator speed (i.e., the generator

frequency ) is decreased. Explain briefly.

Effects of the synchro-check relay parameter settings on the electrical transients and mechanical stress at generator synchronization

In this section, you will set the synchronization parameters of the synchro-check relay to permissive values. You will allow synchronization of the generator to the ac power network. You will observe the generator voltage, current, power, and torque, the bus voltage, and the control signal sent to the circuit breaker at the instant of synchronization. You will repeat this process a few times, then disconnect the synchronous generator from the ac power network. You will set the synchro-check relay to restrictive synchronization conditions, and allow generator synchronization to the ac power network. You will observe the generator voltage, current, power, and torque, the bus voltage, and the control signal sent to the circuit breaker at the instant of synchronization. Finally, you will use the signals recorded on the Oscilloscope to estimate the actual circuit-breaker operate time.

40. Connect Analog Output T of the Four-Quadrant Dynamometer/Power Supply to Analog Input 7/T of the Data Acquisition and Control Interface using a miniature banana plug lead. Connect the common (white terminal) of the Analog Outputs on the Four-Quadrant Dynamometer/Power Supply to an analog (A) common (white terminal) on the Data Acquisition and Control Interface using a miniature banana plug lead.

On the Data Acquisition and Control Interface, remove the miniature banana plug lead connecting Digital Output 2 (DO2) to Analog Input 1 (AI1), then connect Digital Output 1 (DO1) of the Data Acquisition and Control Interface to Analog Input 1 (AI1). This allows the Synchro-Check Relay output signal (i.e., the actual control signal sent by the Data Acquisition and Control Interface to the three-phase contactor) to be observed using the Oscilloscope.




Synchro-Check Relay

Make sure the Voltage Difference E parameter is set to 10% of the ac power network nominal voltage.

Set the Frequency Difference f parameter to 0.5 Hz.

Set the Phase Difference parameter to 50°.

Set the Circuit-Breaker Operate Time parameter to 0.15 s.

Set the Relay Output parameter to Normal.

Speed Governor

Set the Generator Speed Command parameter to 20 r/min below the nominal synchronous speed of the synchronous generator.

a In this part of the exercise, the synchronization conditions are very permissive and result in a relatively long (i.e., loose) synchronization window.

42. On the Oscilloscope, make the required settings to display the generator

voltage (input E2), current (input I2), power (measured via inputs E2 and I2), and torque (measured via Analog Input 7/T), as well

as the bus voltage (input E1). Also, set one of the channels to display the Synchro-Check Relay output signal (available at Analog Input 1 of the Data Acquisition and Control Interface).

a It is recommended to set the time base used to observe the waveforms and signals to 50 ms/div.

On the Oscilloscope, set the trigger type to Hardware, the trigger source to the channel you use to observe the Synchro-Check Relay output signal, and the trigger level to 2 V. Adjust the horizontal position of the trigger point to about 2 divisions from the left-hand side of the Oscilloscope screen.

On the Oscilloscope, click the Single Refresh button.

a These settings ensure that the Oscilloscope begins to record waveforms at the precise moment when the Synchro-Check Relay output signal passes from 0 V to 5 V to initiate generator synchronization.


Wait for the , E, f, , , and SYNC. indicators in the Synchronous Generator Control window to light up permanently, indicating that the synchronous generator is synchronized. The waveforms and signals recorded at generator synchronization should appear on the Oscilloscope screen.



Store all recorded waveforms and signals in the first memory of the Oscilloscope by clicking on the M1 button.

a Alternatively, you can save all waveforms and signals recorded on the Oscilloscope by making a screen capture of the Oscilloscope and saving it to a file.

44. You can repeat the generator synchronization process if desired. To do so, perform steps 45 to 47. Otherwise, go to step 48.

45. In the Synchronous Generator Control window, set the Relay Output parameter to Low to force disconnection of the synchronous generator from the infinite bus.

In the Synchronous Generator Control window, set the Generator Speed Command parameter to 20 r/min below the nominal synchronous speed of the synchronous generator. Wait for the synchronous generator speed to stabilize.


46. In the Synchronous Generator Control window, set the Relay Output parameter to Normal.


Wait for the , E, f, , , and SYNC. indicators in the Synchronous Generator Control window to light up permanently, indicating that synchronous generator is synchronized. The waveforms and signals recorded at generator synchronization should appear on the Oscilloscope screen.

Store all recorded waveforms and signals in the first memory of the Oscilloscope by clicking on the M1 button.








Synchro-Check Relay

Set the Voltage Difference E parameter to 5% of the ac power network nominal voltage.




a In this part of the exercise, the synchronization conditions are much more restrictive and allow for a relatively short (i.e., tight) synchronization window.



Store all recorded waveforms and signals in the second memory of the Oscilloscope by clicking on the M2 button.


51. You can repeat the generator synchronization process if desired. To do so, perform steps 52 to 54. Otherwise, go to step 55.




53. In the Synchronous Generator Control window, set the Relay Output parameter to Normal.





Store all recorded waveforms and signals in the second memory of the Oscilloscope by clicking on the M2 button.


55. In the Synchronous Generator Control window, set the Relay Output parameter to Low to force disconnection of the synchronous generator from the infinite bus, then set the Generator Speed Command and Generator Voltage Command parameters to 0. Wait for the hydraulic turbine driving the generator to stop rotating, then stop the hydropower generator by clicking the Start/Stop button or by setting the Status parameter to Stopped.

In the Four-Quadrant Dynamometer/Power Supply window, stop the hydraulic-turbine emulator by clicking the Start/Stop button or by setting the Status parameter to Stopped.


56. Using the recorded waveforms and signals you stored in the memories of the Oscilloscope (or alternatively, using the screen captures of the Oscilloscope you saved to files), compare the magnitude of the current and power transients recorded at the instant of generator synchronization when the synchro-check relay is set to permissive synchronization conditions to the magnitude of the current and power transients recorded at the instant of generator synchronization when the synchro-check relay is set to restrictive synchronization conditions. What do you observe?



How do the synchronization conditions set on the synchro-check relay affect the current and power transients observed at the instant of generator synchronization?

57. Using the recorded waveforms and signals you stored in the memories of the Oscilloscope (or alternatively, using the screen captures of the Oscilloscope you saved to files), compare the magnitude of the torque transient recorded at the instant of generator synchronization when the synchro-check relay is set to permissive synchronization conditions to the magnitude of the torque transient recorded at the instant of generator synchronization when the synchro-check relay is set to restrictive synchronization conditions. What do you observe?

How do the synchronization conditions set on the synchro-check relay affect the mechanical stress imposed on the synchronous generator shaft at the instant of generator synchronization?

58. Using the vertical cursors of the Oscilloscope, measured the actual circuit-breaker operate time, i.e., the time needed for the circuit breaker to close after it has received the control signal from the synchro-check relay.

Actual circuit-breaker operate time s

59. In LVDAC-EMS, close the Oscilloscope.



Active and reactive power control of a turbine-driven generator after connection to a live infinite bus

In this section, you will make the required settings for manual control of the vane opening and the firing angle of the thyristor three-phase bridge, allowing the generator speed and voltage to be controlled manually. You will synchronize the synchronous generator to a live infinite bus (i.e., the local ac power network). You will then observe what happens to the three-phase active power supplied by the synchronous generator as you vary the vane opening of the hydraulic-turbine emulator. You will also observe what happens to the three-phase reactive power exchanged by the synchronous generator as you vary the firing angle of the thyristor three-phase bridge. You will analyze the results.

60. In the Four-Quadrant Dynamometer/Power Supply window, set the Vane Control parameter to Slider. This allows manual control of the generator speed by adjusting the opening of the adjustable vane in the hydraulic-turbine emulator.


Synchro-Check Relay

Set the Voltage Difference E parameter to 10% of the ac power network nominal voltage.





Set the Thyristor Bridge Firing Control Mode parameter to Manual. This allows manual control of the generator voltage by adjusting the firing angle of the thyristor three-phase bridge providing the generator field current.

62. In the Metering window, make the required settings in order to measure the synchronous generator three-phase active power [metering function PQS2 (E2, I2) 3~], as well as the synchronous generator three-phase reactive power [metering function PQS2 (E2, I2) 3~].






64. In the Four-Quadrant Dynamometer/Power Supply and Synchronous Generator Control windows, adjust the vane opening of the hydraulic-turbine emulator using the Vane Hydraulic Servomotor Control slider and the

generator field current using the Thyristor Bridge Firing Angle parameter so that the generator frequency and voltage are close to the nominal values.

Wait for the , E, f, , , and SYNC. indicators in the Synchronous Generator Control window to light up permanently, indicating that the synchronous generator is synchronized.

65. Record (in the spaces below) the vane opening of the hydraulic-turbine emulator and the thyristor three-phase bridge firing angle indicated in the Four-Quadrant Dynamometer/Power Supply and Synchronous Generator Control windows. Also record the synchronous generator three-phase active power and reactive power indicated by the corresponding meters in the Metering window.

Vane opening of the hydraulic-turbine emulator %

Thyristor three-phase bridge firing angle °

Synchronous generator three-phase active power W

Synchronous generator three-phase reactive power var

Comment the values of the synchronous generator three-phase active power and reactive power you just recorded.

66. In the Four-Quadrant Dynamometer/Power Supply window, increase the vane opening of the hydraulic-turbine emulator using the Vane Hydraulic Servomotor Control slider. While doing so, observe the generator parameters in the Generator Control and Metering windows.

Do not let the synchronous generator operate for a long time at active power values

above 200 W as this could damage the Synchronous Motor/Generator.

In the Four-Quadrant Dynamometer/Power Supply window, decrease the vane opening of the hydraulic-turbine emulator until it is a little below the value recorded in the previous step. While doing so, observe the generator parameters in the Generator Control and Metering windows.



67. What happens to the synchronous generator speed and frequency as you vary the vane opening of the hydraulic-turbine emulator? Explain briefly.

What happens to the synchronous generator active power as you vary the vane opening of the hydraulic-turbine emulator? Explain briefly.

a Do not take into account the variation in the synchronous generator reactive power as you vary the vane opening of the hydraulic-turbine emulator. The reasons behind this reactive power variation are beyond the scope of this manual.

68. In the Four-Quadrant Dynamometer/Power Supply window, adjust the vane opening of the hydraulic-turbine emulator using the Vane Hydraulic

Servomotor Control slider so that the amount of active power supplied by the generator is as close as possible to 0 W.

69. In the Synchronous Generator Control window, increase the generator field

current by decreasing the Thyristor Bridge Firing Angle parameter. While doing so, observe the generator parameters in the Generator Control and Metering windows.

Do not let the synchronous generator operate for a long time at reactive power values

above 200 var as this could damage the Synchronous Motor/Generator.



In the Synchronous Generator Control window, decrease the generator field

current by increasing the Thyristor Bridge Firing Angle parameter until it is a little above the value recorded in step 65. While doing so, observe the generator parameters in the Generator Control and Metering windows.

70. What happens to the generator voltage as you vary the generator field current using the firing angle of the thyristor bridge? Explain briefly.

What happens to the synchronous generator reactive power as you vary the generator field current using the firing angle of the thyristor bridge? Explain briefly.

71. In the Four-Quadrant Dynamometer/Power Supply and Synchronous Generator Control windows, adjust the vane opening of the hydraulic-turbine emulator using the Vane Hydraulic Servomotor Control slider, and the generator field current using the Thyristor Bridge Firing Angle so that the

generator active power and reactive power are as close as possible to 0.

In the Synchronous Generator Control window, set the Relay Output parameter to Low to force disconnection of the synchronous generator from the infinite bus.

72. In the Four-Quadrant Dynamometer/Power Supply window, close the vane completely using the Vane Hydraulic Servomotor Control slider. Wait for the hydraulic turbine driving the generator to stop rotating, then stop the hydraulic-turbine emulator by clicking the Start/Stop button or by setting the Status parameter to Stopped.

Exercise 2 – Generator Synchronization Using a Synchro-Check Relay Conclusion


In the Synchronous Generator Control window, stop the hydropower generator by clicking the Start/Stop button or by setting the Status parameter to Stopped.


73. Close LVDAC-EMS, then turn off all the equipment. Disconnect all leads and return them to their storage location.

In this exercise, you were introduced to the synchronization of a three-phase synchronous generator to a live ac power system (i.e., a live bus) using a synchro-check relay. You became familiar with the operation of a synchro-check relay as well as with the main synchronization parameters of a synchro-check relay, such as the frequency difference ( f), voltage difference ( E), and phase angle difference ( ). You learned how to connect a three-phase synchronous generator to a dead bus using a synchro-check relay.

1. What is a synchro-check relay? Explain briefly.

2. What are the three main synchronization parameters of a synchro-check relay used to synchronize a generator to a live bus? Explain each one briefly.

CONCLUSION

REVIEW QUESTIONS

Exercise 2 – Generator Synchronization Using a Synchro-Check Relay Review Questions


3. Why is it important for a synchro-check to ensure that the synchronization window is longer than the circuit-breaker operate time parameter before the relay allows generator synchronization? Explain briefly.

4. What is the distinction between a live bus, an infinite bus, and a dead bus? Explain briefly.

5. Briefly explain how a synchro-check relay verifies that a bus is dead, and then how it connects a synchronous generator to the dead bus.

Documents

Hydropower Electricity Generation, 2 Generator ... as well as with the main synchronization parameters of a synchro-check relay, such as the frequency difference ( ûf), voltage difference