DK1913_CH16

16RELAY COORDINATION STUDIES

16.1 INTRODUCTION

In a power system, the protective devices are used to protect the system in theevent of a fault. The function of protective devices in a power system is to detectsystem disturbances and isolate the disturbance by activating the appropriatecircuit-interrupting devices. A protection coordination study is required toproperly select the protective devices and specify the necessary settings so thatthe intended goals will be achieved. In the classical studies, the time currentcoordination was performed using the manual methods. With the introduction ofpersonal computers in the workplace along with software to perform thecoordination functions, computer-aided approaches are now used. Selectivity,coordination, speed and reliability are the important features of the protectiondevices as explained below [1,2].

Selectivity - For a protective system, a general term describing the interrelatedperformance of relays and other protective devices, whereby a minimum amountof equipment is removed from service for isolation of a fault or otherabnormality. Selectivity is a desirable characteristic in any protection scheme.However, it is not always possible to obtain the desired degree of system andequipment protections in a selective fashion. Usually an optimum setting isachieved for satisfactory performance.

Copyright 2002 by Marcel Dekker. All Rights Reserved.

Coordination - This term is sometimes used to describe a reasonablecompromise based on an engineering evaluation, between the mutually desirablebut competing objectives of maximum system protection and maximum circuitcurrent availability. The protective device ratings and settings recommendedfrom an exercise must be the best balance between these factors.

Speed - Speed is the ability of the relay to operate in the required time period.The speed is important in fault clearing since it has direct impact on the damagedone due to the short circuit current. The ultimate aim of protective relaying is todisconnect the faulted equipment as quickly as possible.

Reliability - It is important that the protective relaying be reliable. Thereliability of the protective relaying refers to the ability to perform accuratelywhenever a fault occurs in the system. The protective relaying and associatedpower supplies have to be very reliable and should not fail in the event of afailure in the power system.

The following is a generally accepted approach for selecting and settingprotective devices:

• A first-zone or primary protective device will remove a faulty circuit asquickly as possible. This is called primary protection.

• If the primary protection fails, a back-up protective device will remove thefault. An upstream device that acts as the primary device in its zone usuallyprovides the back-up function. Therefore, the current coordination isrequired between the primary and back-up protective devices.

• The protective device settings are individually chosen to accommodate thecircuit parameters. The criteria used in determining the recommendedsettings for the protective devices are based on system currents, allowablemargins and applicable industry standards.

16.2 APPROACH TO THE STUDY

The most convenient way of determining the proper ratings and settings ofprotective devices such as low voltage power circuit breakers, fuses and relays isby plotting the time-current curves. These curves are drawn on standard log-loggraph and illustrate the time-current characteristics of each of the protectivedevices as well as the protective criterion to be met. Thus, such curves illustratethe time-current coordination between devices. Time-current curves are generallydrawn up to the maximum available fault current level for the system being


illustrated. In practical power systems, with the change in the configuration, themaximum available fault will increase. It is important that the results of the studybe reviewed and updated at periodic intervals.

Although the time-current curves may be drawn, this step is not necessary if theprotective devices involved are all overcurrent relays. Instead, it is possible todetermine the selectivity by comparing at most three critical values of faultcurrent and the associated relay operating times. Sometimes, the relay settings aredetermined based on analytical calculations.

Regardless of the approach used to determine the relay settings, it must berecognized that the operating time of overcurrent protective relays is notpredictable for magnitudes of current only slightly greater than rated pickupcurrent. For this reason, definite electromechanical relay time-currentcharacteristics are rarely shown below 1.5 times pickup and it is this magnitudeof current which is considered the maximum sensitivity when using the analyticaltechnique. In microprocessor relays, practically any setting is possible dependingon the specific relay and application. In the past, the one line drawings wereprepared in the drawing office. The time current coordination curves were alsoprepared in the drawing office. All the required explanations and comments arepresented as required in the drawings.

16.3 ACCEPTANCE CRITERIA

The primary function of a protective device is to protect the circuits and equipmentduring abnormal operating conditions. Therefore, it essential to know the equipmentprotection boundaries to determine the necessary settings. The maximum loadcurrent and the short circuit current determine the maximum upper boundaries ofthe current sensitivity within which the circuit protective devices must operate. Therequired operating boundaries are given by:

• Operating conditions.• Minimum protection level.• Equipment withstand level.

Operating conditions - The protective devices must be insensitive to the normalequipment currents including the full load current, allowable overload current andstarting current. Such data is available for every equipment on the nameplate orapplicable industry standard. The data for some of the common equipment arediscussed below.

Induction motors - The full load current of a motor can be determined from the


following equation:(hp) (0.746)

I (foil load) = -7= ^^ - (16.1)V3 (Efficiency) (Power Factor) (kV)

Permissible overload for motors - This is a function of the motor service factorand temperature. For a service factor of 1.1, the overload capability will be 1.1 perunit.

Starting current of induction motors - The starting current of an induction motorwill be equal to the locked rotor current. Usually, the locked rotor current will beequal to six times the rated current. For wound rotor induction motors, the lockedrotor current will be four times the rated current.

Minimum protection requirement - For motors 600 V and below the NEC [3]requires overload and overcurrent protection. The required overload protection formotors is given by:

Motors with service factor not less than 1.15 =125%Motors with temperature rise not over 40 degree C - 125%All other motors = 115%

Sometimes, additional protection limits are given for multi-speed motors and otherspecial motors. The phase overcurrent devices are set to trip at the following limits:

Inverse time circuit breaker = 250%Instantaneous trip circuit breaker = 700%No time delay fuses = 500%Dual element time delay fuses = 175%

If the overload and short circuit protection is part of a controller, the short circuitprotection can be set to 1300%.

Motor withstand level - This is the maximum allowable stall time, the time up towhich the motor can continue to operate in stalled condition before damage occurs.This time is expressed in seconds.

Transformers - The full load current of a transformer can be calculated using theequation:

kVAI (full load) = -/= (16.2)

V3(kV)


Permissible overload for transformers - The overload capability of atransformer depends on the type of cooling and the following classes are available:

AA - Self cooled ventilated dry type AFA - Fan cooled ventilated dry typeOA - Self cooled, oil SA - Self cooled, siliconeVA - Self cooled, vapor CFA - Fan cooled, oilVFA - Fan cooled, vapor CFOA - Fan and oil pump cooled, oil

The transformer capability is the full load amperes multiplied by the cooling factorand temperature rise factor, if any.

Transformer inrush current - The transformers draw significant inrush currentduring energization. For transformers with fuses in the primary circuit forprotection, the limiting condition has to be observed. The primary fuse has to bechosen such that the fuse will not melt due to inrush current. Table 16.1 summarizesthe allowable transformer inrush current and the duration as per ANSI StandardC57.12.

Table 16.1 Transformer Inrush Current and Duration

MVA Inrush Duration, second

<3MVA>3MVA

8 x Rated current12 x Rated current

0.10.1

Article 240-100 of the 1999 National Electrical Code [3] states that, forovercurrent protection of feeders above a nominal 600 volts, 'In no case shall thefuse rating in continuous amperes exceed three times, or the long-time tripelement setting of a breaker six times, the ampacity of the conductor'. The codecontains tables of ampacity ratings published by the Insulated Power CableEngineers Association (IPCEA). Article 450-3 of the 1999 NEC providesdetailed requirements for transformer protection. These requirements forprotective device ratings or settings in multiples of full load current are presentedin Table 16.2.


Table 16.2 Maximum Current Ratings for Fuse and Circuit Breakers

TransformerImpedance

All<6%

>6% and <10%All

<6%>6% and < 1 0%

PrimaryVoltages

>600 V

<600 V

Transformer PrimsMaximum

Circuit BreakerRatino

3X6X4X3X6X4X

rv Side

MaximumFpse Rating

2X3X3X

2.5X6X4X

Transformer Secondary SideAbove 600 V

Maximum CBRatingNone3X

2 5XNoneNone2.5X

MaximumFuse Rating

None2.5X2 5XNoneNone2 25X

600V & AboveMaximum

CB/Fuse RatingNone1.25X1.25XNone1.25X2.25X

It should be noted that NEC code permits a primary feeder protective device tooffer the defined transformer primary protection. In some cases a circuit breakerand the associated relaying can be used to protect several transformers.

The ANSI curve, which can be shown on the time current curves, represents theamount of mechanical and thermal stresses a distribution power transformer isrequired to withstand without any damage as specified by ANSI StandardC57.12, 1973 [4]. The ANSI standard C57.109 [5] defines the short circuitthrough fault withstand current and time limits for four categories of transformers(see Table 16.3).

Table 16.3 Transformer Withstand Current and Time Limits [5]

Category

I

II

III

IV

Transformer kVASingle Phase

5 to 25

37.5 to 100

167 to 500

501 to 1667

1668 to 10000

Above 10000

Three Phase

15 to 75

11 2.5 to 300

500

501 to 5000

5001 to 3 0000

Above 30000

Through Fault Withstand CapabilityBase Current, PL)

4 0 o r l / Z t ( l )

35 or l /Z t ( l )

25 or l / Z t ( l )

1/Zt

l/(Zt + Zs)

l/(Zt + Zs)

Time, Seconds

1250X

1250X

1250X

2#

2#

2#

Notes:(1)ZtZsX#

- Choose the smaller value- Transformer impedance in per unit based on self cooled rating- System per unit impedance on transformer base- (Chosen per unit base current)"- These points define an I2 t curve in the short time region which isfrom 70% to 100% of maximum through fault current for category IIand 50% to 100% for category III and category IV.


Transformer withstand levels - In order to express the damage withstand level,the current distribution during various type of faults are needed. In the transformercircuits, the current through winding depends on the type of connection. Thecurrents through various transformer connections are presented in Figure 16.4.

Table 16.4 The Current Through Transformer Windings During Faulted Conditions

Primary Secy.

A^AT£

AA-< -<

Factor

L-L0.87

L-G0.58

L-L0.87

L-L0.87

Primary Secondary

~~*\ """K

-< A

-£ -£7$ A

Factor.

L-L0.87

L-L0.87

L-L0.87

L-L0.87

Cables - The full load current is determined by the size of the cable conductor andthe derating factors as given by the industry standards. There are several types ofcables available for the low-voltage, medium-voltage and high-voltage applications.The overload capability of the cable depends on the installation media and theloading factor. The permissible overcurrent setting is as per NEC article 240-3,1999 [3].

16.4 COMPUTER-AIDED CORDINATION ANALYSIS

There are several computer programs available for the protection coordinationanalysis of power system applications. Such programs include short circuit analysisand device time current characteristics. The main purpose of the protectivecoordination software is to produce one-line diagrams, calculation of relay settingsand time current coordination drawings. Software will contain features to modelvarious protective devices, equipment damage curves and store the data for futureuse. Using the software, the device characteristics can be called from the libraryand used for the coordination studies. These programs are used in the utility,industrial, commercial and other power supply installations.


Personal computer - A personal computer, either stand alone or connected to anetwork with sufficient memory is needed for this type of application. Also, agood graphical monitor and laser quality printer is required. By performing thestudy on a personal computer, several alternatives can be examined beforearriving at the final solution. The data can be stored in the computer for futureuse or verification of the calculations. The one-line drawings, TCC and theoutput can be printed for a report. Alternatively, these files can be copied andpasted in word processing documents.

Graphical display - The one-line diagram of the electrical circuit and the devicecoordination curves can be displayed on the graphical monitor for demonstration.Such a display helps to identify the necessary corrections to be performed beforegetting a printout of the diagrams or graphs. Also, the one-line drawings can beprepared with the calculated relay settings. Such an approach eliminates the need todeal with the drawing office. Further, the graphical drawings can be expanded toview the details using the zoom function.

One-line diagram - A one-line diagram of the electrical circuit for which thecoordination is performed is always needed for report preparation. The software canbe used to prepare the one-line diagram with the necessary devices shown. Such anapproach eliminates the need to deal with the drawing office support for theprotection study.

Project data files - A database is a method of storing digital data. The databasecan be structured to store all the necessary device characteristics, short circuit dataand coordination data. These programs can perform calculations of the inrushcurrent, device settings and project details. The project data can be copied fromone computer to another for analysis.

Device library - These programs are equipped with a large library of data fromvarious manufacturers. The library includes models for overcurrent relays, groundrelays, static trip breakers, molded case circuit breakers, data for cable damagecurve, data for transformer damage curve, motor overloads and reclosers. Theprograms use curve fitting techniques to model the time curve coordinationcharacteristics. Such data libraries are very useful in performing the coordinationstudies since the verified data are readily available.

Interactive data entry - It is not always possible to have the data available fromthe device library for the selected study. If the data are not available and if theequation or graphical data are available, then the data can be entered interactively.The data points can be entered item by item and can be saved for future use. Thesoftware also provides the opportunity to modify the data by changing the device


settings, multipliers and other parameters without leaving the program. The editeddata can be stored for future use.

Some of the other features of the computer-aided analysis are:

• Display of TCC and edited one-line drawings together.• Automatic display of labels in the one-line diagrams.• Device at various voltage levels can display in the same graph.• Display of common errors such as wrong voltage or current ratings.• Plots can be printed in log-log graphs or in plain sheets.

16.5 DATA FOR COORDINATION STUDY

The one-line diagram of the power system for which the coordination study isperformed is required and should clearly identify the following:

• Incoming circuits.• Transformer voltages, MVA, connection (delta/wye etc.), grounding and

ground protection.• Protection relay designation number.• Fuses or circuit breakers in the incoming lines.• Secondary bus voltage, breakers and fuses.• Circuit breaker specifications.• Feeder and distribution protection devices.• Motor control centers and breaker or fuse ratings.

The short circuit results are needed from the protection coordination study. Someprograms can perform the short circuit calculations and can use the results in theprotection coordination studies. Some of the required data and the correspondingconversion to get the data suitable for protection study are discussed below.

Transformer data - The transformer nameplate data are required for the relaycoordination analysis. Whenever the complete data are not available, then thelibrary data can be used knowing the MVA rating of the equipment. An exampleof data for the transformer is presented in Table 16.5.


Table 16.5 Transformer Data for Protection Analysis

Description

Transf.

Rated InrushkVA kV A P.U. Z, % Connection

2000 4.16/0.48 278 8.0 5.75 Del/Wye-g

The transformer nameplate data are then converted to get the necessary detailsfor the relay coordination studies. Such data include the ANSI curve at theprimary and the secondary inrush current. The transformer damage curve can beconstructed based on the ANSI standard C57.109. An example damage curve fora 2000 kVA transformer is shown in Figure 16.1. The rated current of thistransformer is 278 A as is shown. The rated secondary current of this transformeris 2,405 A. The inrush current of this transformer is around 20,000 A and isshown in the graph.

Motor data - The nameplate details of the motor are collected and the ratedcurrent and locked rotor current values are identified. An examples of data ispresented in Table 16.6.

Table 16.6 Motor Data for Protection Analysis

Description kVA Volt I, A Efficiency Type Power Factor

Motor Ml 250 480 241 0.93 Ind. 0.8

Using these data, the locked rotor current, momentary and interrupting currentcontributions for a short circuit are calculated for the protection study.

Cable data - There are several types of cables available for all types of powersystem application. The manufacturer data are to be followed closely to ensurethe accurate specifications. An example of cable data is presented in Table 16.7.

Table 16.7 Cable Data for Protection Analysis

Qty/ AllowedDescription Volt Phase Size Length Material Temp.

Feeder 4.16W 2 1/0 120' Copper 150deg.C


Using these data, the circuit impedance is evaluated for each section of the cablein per unit. Also, the cable damage curve is required for the TCC analysis.

Circuit breaker data - For low voltage applications there are circuit breakerswith static trips, ground fault protectors, molded case circuit breakers and powercircuit breakers. The nameplate specifications of the circuit breaker are collectedfor the protection study. Sample data are shown in Table 16.8.

1000

CURRENT IN AMPERES

|278 A .

100

2000.0 kVAType: DTPri Conn DeltaPri Tap -2.50 %Sec Conn Wye-GroundSec Tap 0.00 %

10

0.10TX Inrush

X

0.010.5 1 10 100 1K

XFMR.tcc Ref. Voltage: 480 Current Scale X 10A2

10K

Figure 16.1 The Transformer Damage Curve and the Related Data(Courtesy of SKM System Analysis, Inc., Output from Power Tools for Windows

Program)


Table 16.8 Circuit Breaker Data for Protection Analysis

System CB Size TripDescription V V A A Trip Type

Bl 480 600 150 600 Static

Using these data, the necessary data for the circuit breaker relaying are identified.The relaying may be phase overcurrent relay, ground fault relay or both. Sampletime current coordination characteristics of the overcurrent relay for a circuitbreaker are shown in Figure 16.2.

CURRENT IN AMPERES

1000

100

B-SWBD1

0.010.5 1 10 100 1K

B-SWBD1.tcc Ref. Voltage: 480 Current Scale X 10A1

10K

Figure 16.2 Sample Time Current Coordination Curve of a Circuit Breaker(Courtesy of SKM System Analysis, Inc., Output from Power Tools for Windows

Program)


Relay data - The overcurrent relay is one of the basic devices used in the powersystem for the protection from overloads. The relay operates when more than theset value of current flows through a circuit. The two basic overcurrent relays usedin the power system are instantaneous and the time delay types. Theinstantaneous overcurrent relay is designed to operate with no time delay whenthe circuit current exceeds the relay setting. The operating time of this type ofrelay will be of the order of 0.1 second. The time overcurrent relay has inverseoperating characteristics as shown in Figure 16.3. The specific characteristicsmay be moderately inverse, normal inverse, very inverse or extremely inverse asper ANSI C37.90. The application and relay setting calculations are explainedfor various types of relays in Reference [6]. The typical relay data include thefollowing:

• The circuit where the circuit breaker is located.• Voltage rating of the circuit.• ANSI device number of the relay.• Manufacturer of the relay.• Type number of the relay.• The range of relay settings recommended for this device.• The current transformer ratio.• The multiplier, M.• The value of the pick up current in A [pick up current = (CT ratio) (M)].• The time delay involved in the instantaneous relay.• The magnitude of the instantaneous current.

Extremely Inverse

Very Inverse

Inverse

Instantaneous

Multiples of Pickup Current

Figure 16.3 Time Current Characteristics of Overcurrent Relays

Sample data for overcurrent relay setting are presented in Table 16.9.


Table 16.9 Sample Overcurrent Relay Settings

CircuitCB1

kV4.16

ANSIDevice50/5150G

MfgABCABC

RelayNo.

RellRel2

RelaySettings

0.9CT, NI, M=l

0.2 CT,0. Is delay

CTRatio

1200/5

50/5

Recommended Settings

M1

1

Pick UpAmp1000

10

Usually the time overcurrent curves are identified for each relay location beforeperforming the coordination studies.

Fuse data - A fuse is a device with a fixed continuous current rating with adefinite interrupting current rating. There are a variety of fuses available for thepower system applications both in the low-voltage and medium-voltage levels.There are two types of fuses used in the power system protection, the currentlimiting type and the expulsion type. The current limiting fuses are capable ofmelting and clearing high fault currents faster than 0.01 second. The expulsiontype fuses in general do not limit current and must wait until the first naturalcurrent zero before the fault clearing. The fuses are used for the protection oftransformers, motors and other loads in individual circuits. Sample time currentcoordination curve of a fuse is shown in Figure 16.4.

Example 16.1 - Consider a radial power system supplied from a 13.8 kV source.The step-down transformer (TX E) is 3,000 kVA, 13.8 kV/4.16 kV, delta/wye-grounded. The high voltage fuse is (F4) is rated to 4.16 kV, frame 250 A. Thedistribution transformer (TX G) is 2,000 kVA, 4.16 kV/480 V, delta/wye-grounded. The fuse in the transformer circuit (F TX G) is 600 V, frame 150 A.The circuit breaker (LVP5) is 600 V and frame 400 A. The motor controller(M28) is rated for 600 V and frame 250 A. The circuit is connected to a 250 kVAmotor load. Perform a study using computer-aided software.

Solution - The protection coordination problem is solved by using the PowerTools for Widows (PTW) program from SKM System Analysis, Inc. This is apopular program the distribution system analysis with library data fortransformers, circuit breakers, reclosers and fuses from various manufacturers. Aone-line diagram of the system is prepared using the graphics program. Thenusing the component editor program, the data for various components are editedor called from the library data. An example window showing the circuit breakerdata display is shown in Figures 16.5. Also, the time current coordination curvefor each of the protection device is extracted from the library data. The TCCcurves of the transformer, circuit breaker and the fuse are shown in Figures 16.1,16.2 and 16.4 respectively.


CURRENT IN AMPERES

1000

10

0.01

S&CSM-4, 50ESensor/Trip 50.0 A

0.5 1 10 100 1K

Fuse.tcc Ref. Voltage: 4160 Current Scale X 10A1

10K

Figure 16.4 Time Current Coordination Curve of a Fuse(Courtesy of SKM System Analysis, Inc. Output from Power Tools for Windows

Program)

Then the program is executed and the output results are obtained. The programoutput contains the following:

• One-line diagram of the system, including the relay settings, shown in Figure16.6.

• The settings of the protective devices, shown in Table 16.10.• The time current coordination curve (TCC), shown Figure 16.7.

The TCC curve of the transformer (damage curve), the fuse (F TX 3), circuitbreaker (B-SWBD1) and the circuit breaker (LVP1) are presented in the samegraph.


Figure 16.5 Window for Input Data of a Circuit Breaker with Static Trip(Courtesy of SKM System Analysis, Inc.)

16.6 CONCLUSIONS

The protection coordination study involves the preparation of the one-linediagram of the system, identifying the protective relay characteristics of variousdevices, calculation of the short circuit results and the relay settings. Thoughsome these calculations are simple, the overall coordination study involves manycalculations, preparing one-line diagrams, and preparing superimposed TCCcurves for various devices. Therefore, a computer-aided analysis with the aid of agraphics package and database support is a very valuable tool for this study. Inthis Chapter, the approach to the protection coordination study, the datacollection and the presentation of the results are analyzed. It can be seen thatusing the computer-aided approach, the protection coordination study can beperformed quickly, though there is a need for training on the use of the givenprogram. A computer-aided analysis of a small distribution system example isshown. The analysis was performed using commercially available software andthe program output provides the following:

• One-line diagram of the system with relay settings.• The summary of the calculated results and the settings.• The combined time current coordination curve (TCC).


The final coordination results are to be judged by the manual methods in order toensure the accuracy. The protective device number of various items is presentedbelow for ready reference.

007-TX E PRI

SIEMENSPri CT 400 ASec CT 1 AISGSSettings

LTPU 2.6INVERSE 1.85INST 20.0

GOULD SHAWMUTCL-14, 250EFrame 250.0 A

T Sensor/Trip 250.0 AVSJ^AJ

GOULD SHAWMUTCL-14, 150EFrame 150.0 ASensor/Trip 150.0 A

GETLB4Frame 400.0 ASensor/Trip 300.0 ASettings

Thermal Curve (Fixed)INST (4.5-10 x Trip) 9.0

CUTLER-HAMMERMCPFrame 250.0 ASettings

INST(1250-2500A)2185A

TXG

F TX G SEC

027-DSB 3

C13B

LVP5

028-MTR 28 B

MCP M28 #3

M28#3

Figure 16.6 One Line Diagram of the Example(Courtesy of SKM System Analysis, Inc.)


Table 16.10 Output of the Program Run - Edited Version(Courtesy of SKM System Analysis, Inc.)

(Output from the Power Tools for Windows Program)

TCC Name: Mtr28.tecReference Voltage: 4160Current Scale X 10*1

ALL INFORMATION PRESENTED IS FOR REVIEW, APPROVAL, INTERPRETATION,AND APPLICATION BY A REGISTERED ENGINEER ONLY.CAPTOR {Computer Aided Plotting for Time Overcurrent Reporting)COPYRIGHT SKM SYSTEMS ANALYSIS, INC. 1983 - 2000

Device Name: TXDescription:Nominal Size:Impedance (%Z) :Inrush Factor:

3 Bus Name: 026-TX G PRI2-Winding Transformer Damage Curve2000.0kVA5.74998 .Ox

TCC Name: Mtr28.tecBus Voltage: 4160V / 480V

DeltaWye-Ground

Device Name: F 4Manufacture: GOULD SHAWMUTSub Type: CL-14, 5 . 5kv E-Rated

Bus Name: 026-TX G PRI TCC Name: Mtr28.tecDescription: 10E-600E

AIC Rating: 63kACartridge: CL-14, 250E 5500V 250A 63kASize: 250A

Device Name: CIO Bus Name: BLDG 115 SERVDescription: Cable Damage CurveSize: 1/0Material: CopperQty/Ph: 2

Device Name: R7 SEC Bus Name: BLDG 115 SERVManufacture: SIEMENSSub Type: ISGS 1AClass Description: ISGSAIC Rating: N/ACurrent Rating: 400A / 1ASetting: 1) LTPU 2.6

2) INVERSE 1.853) INST 20.0

Adder: 0.5000 Shifter: 2.0000

Device Name: M28 #3 Bus Name: 028-MTR 28 BDescription: Motor Starting CurveRated Sized: 250KVA (1 of 1 Plotted)FLA+Load Adder: 300.7A + O.OAPower Factor: 0.830Efficiency: 0.93

Device Name: MCP M28 #3 Bus Name: 028 -MTR 28 BManufacture: CUTLER-HAMMERSub Type: MCP

Bus Voltage: 4160.0VFault Duty: 6840. 9ACurve Multiplier: 1.00000

TCC Name: Mtr28.tccBus Voltage: 4160V

Cont . Temp; 150 deg C.Damage Temp: 190 deg C.

TCC Name: Mtr28 .tecDescription: SECONDARY

Bus Voltage: 4160.0VFault Duty: 7019. 1ACurve Multiplier: 1.00000Test Points:82. OX, 11.334s(S5.0X, 2.398s

TCC Name: Mtr28 .tecBus Voltage: 480V

Inrush: 0.0 (O.OA!Starting Time: 5.00sFull Voltage (Square Transient)

TCC Name: Mtr28 .tecDescription: 250A (1250-2500A

AIC Rating: 30Frame: MCP 480V 250A 30kACurrent Rating: OA / OASetting: 1) INST (1250-2500A) 2185A

Bus Voltage: 480.0VFault Duty: 21503.0ACurve Multiplier: 1.00000FLA: 0.OA


Figure 16.7 Time Current Coordination Curve (TCC)(Courtesy of SKM System Analysis, Inc.)

(Output from the Power Tools for Windows Program)

ANSI STANDARD DEVICE FUNCTION NUMBERS

Device # Function1. Master Element2. Time-delay Starting or Closing Relay3. Checking or Interlocking Relay4. Master Contractor5. Stopping Device6. Starting Circuit Breaker7. Anode Circuit Breaker8. Control-Power Disconnecting Service9. Reversing Device10. Unit Sequence Switch11. Reserved for future application12. Over-speed Device13. Synchronous-Speed Device


14. Under-Speed Device15. Speed-or Frequency-Matching Device16. Reserved for future application17. Shunting or Discharge Switch18. Accelerating or Decelerating Device19. Starting-to-Running Transition Contractor20. Electrically Operated Valve21. Distance Relay22. Equalizer Circuit Breaker23. Temperature Control Device24. Reserved for future application25. Synchronizing or Synchronism-Check Device26. Apparatus Thermal Device27. Undervoltage Relay28. Flame Detector29. Isolating Contractor30. Annunciator Relay31. Separate Excitation Device32. Directional Power Relay33. Position Switch34. Master Sequence Device35. Brush-Operating or Slip-Ring Short Circuiting Device36. Polarity or Polarizing Voltage Device37. Undercurrent or Underpower Relay38. Bearing Protective Device39. Mechanical Condition Monitor40. Field Relay41. Field Circuit Breaker42. Running Circuit Breaker43. Manual Transfer or Selector Device44. Unit Sequence Starting Relay45. Atmospheric Condition Monitor46. Reverse-Phase or Phase-Balance Current Relay47. Phase-Sequence Voltage Relay48. Incomplete-Sequence Relay49. Machine or Transformer Thermal Relay50. Instantaneous over Current or Rate-of-Rise Relay51. AC Time Overcurrent Relay52. AC Circuit Breaker53. Exciter or DC Generator Relay54. Reserved for future application55. Power Factor Relay56. Field-Application Relay


57. Short Circuiting or Grounding Device58. Rectification Failure Relay59. Overvoltage Relay60. Voltage or Current Balance Relay61. Reserved for future application62. Time-Delay Stopping or Opening Relay63. Pressure Switch64. Ground Protective Relay65. Governor66. Notching or Jogging Device67. AC Directional Overcurrent Relay68. Blocking Relay69. Permissive Control Device70. Rheostat71. Level Switch72. DC Circuit Breaker73. Load-Resistor Contractor74. Alarm Relay75. Position Changing Mechanism76. DC Overcurrent Relay77. Pulse Transmitter78. Out-of-Step Protective Relay79. AC Reclosing Relay80. Flow Switch81. Frequency Relay82. DC Reclosing Relay83. Automatic Selective Control or Transfer Relay84. Operating Mechanism85. Carrier or Pilot-Wire Receiver Relay86. Locking-Out Relay87. Differential Protective Relay88. Auxiliary Motor or Motor Generator89. Line Switch90. Regulating Device91. Voltage Directional Relay92. Voltage and Power Directional Relay93. Field-Changing Contractor94. Tripping or Trip-Free Relay95- 99 Used only for specific applications on individual installations where

none of the assigned numbered functions from 1 to 94 are suitable.


PROBLEMS

1. What are the basic steps required to perform a protective devicecoordination study?

2. A one-line diagram of a radial system is shown in Figure 16.8. The system issupplied through a substation with a short circuit rating of 10,900 A. Thecircuit breakers CB1 through CB5 are shown at various locations andcontain both the phase overcurrent relay and ground current relays. The stepdown transformer Tl is 100 MVA, 69 kV/13.8 kV, wye-grounded/delta andhas 8% impedance. Transformer T2 is 25 MVA, 13.8 kV/4.16 kV,delta/wye-grounded with 10% impedance. The synchronous motor at the13.8 kV bus is 50 MVA, 13.8 kV and 0.95 power factor. There are twoinduction motor loads at the 4.16 kV bus each with 1000 hp, 4.16 kVoperating at a power factor of 0.9. The fuses at the induction motor circuitsare selected to provide protection at rated load. Prepare the data and conducta computer-aided coordination study. Discuss the assumptions made.

69 kVSource

13.8W

CB4

Figure 16.8 One-Line Diagram for Problem 2


3. The transformer damage curve can be prepared from the fundamentalequation. Show the step-by-step calculations for a 2000 kVA, 4.16 kV/460V, delta/wye-grounded transformer with an impedance value of 8.75%.

4. Identify all the leading programs available for the protection coordination ofindustrial systems. Can these programs serve the purpose of performingsimilar studies for transmission systems? Explain your answer.

5. What are the graphical features required for the protection coordinationprogram?

6. Compare and discuss the outputs from the protection coordination programand the output results of manual calculations.

REFERENCES

1. IEEE Standard 141, IEEE Recommended Practices in Electric PowerDistribution for Industrial Plants, 1993 (The Red Book).

2. ANSI/IEEE Standard: 242, IEEE Recommended Practice for Protection andCoordination of Industrial and Commercial Power Systems, 1986.

3. M. W. Earley, J. V. Sheehanand and J. M. Cloggero, National ElectricCode, National Fire Protection Association, Quency, MA 1999.

4. ANSI Standard C57.12, General Requirements for Liquid ImmersedDistribution Power and Regulating Transformers, 1980.

5. ANSI Standard C57.109, IEEE Guide for Transformer Through FaultCurrent Duration, 1985.

6. B. J. Lewis, Protective Relaying Principles and Applications, MarcelDekker, Inc., New York, 1987.

7. Power Tools for Windows, SKM Systems Analysis, Inc., Manhattan Beach,California.


Documents

DK1913_CH16