130101 Power Quality

2013 PETROLIAM NASIONAL BERHAD (PETRONAS)

All rights reserved. No part of this document may be reproduced, stored in a retrieval system or transmitted in any form or by any means (electronic, mechanical, photocopying, recording or otherwise) without the permission of the copyright owner. PETRONAS Technical Standards are Companys internal standards and meant for authorized users only.

PETRONAS TECHNICAL STANDARDS

POWER QUALITY

PTS 13.01.01

MAY 2013

POWER QUALITY

PTS 13.01.01

May 2013

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FOREWORD

PETRONAS Technical Standards (PTS) has been developed based on the accumulated knowledge,

experience and best practices of the PETRONAS group supplementing by national and international

standards where appropriate. The key objective of PTS is to ensure standard technical practice

across the PETRONAS group.

Compliance to PTS is compulsory for PETRONAS-operated facilities and Joint Ventures (JVs) where

PETRONAS has more than fifty percent (50%) shareholding and/or operational control, and includes

all phases of work activities.

Contractors/manufacturers/suppliers who use PTS are solely responsible in ensuring the quality of

work, goods and services meet the required design and engineering standards. In the case where

specific requirements are not covered in the PTS, it is the responsibility of the

Contractors/manufacturers/suppliers to propose other proven or internationally established

standards or practices of the same level of quality and integrity as reflected in the PTS.

In issuing and making the PTS available, PETRONAS is not making any warranty on the accuracy or

completeness of the information contained in PTS. The Contractors/manufacturers/suppliers shall

ensure accuracy and completeness of the PTS used for the intended design and engineering

requirement and shall inform the Owner for any conflicting requirement with other international

codes and technical standards before start of any work.

PETRONAS is the sole copyright holder of PTS. No part of this document may be reproduced, stored

in a retrieval system or transmitted in any form or by any means (electronic, mechanical, recording

or otherwise) or be disclosed by users to any company or person whomsoever, without the prior

written consent of PETRONAS.

The PTS shall be used exclusively for the authorised purpose. The users shall arrange for PTS to be

kept in safe custody and shall ensure its secrecy is maintained and provide satisfactory information

to PETRONAS that this requirement is met.

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ANNOUNCEMENT

Please be informed that the entire PTS inventory is currently undergoing transformation exercise from 2013 - 2015 which includes revision to numbering system, format and content. As part of this change, the PTS numbering system has been revised to 6-digit numbers and drawings, forms and requisition to 7-digit numbers. All newly revised PTS will adopt this new numbering system, and where required make reference to other PTS in its revised numbering to ensure consistency. Users are requested to refer to PTS 00.01.01 (PTS Index) for mapping between old and revised PTS numbers for clarity. For further inquiries, contact PTS administrator at [email protected]

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Table of Contents

1.0 INTRODUCTION ..................................................................................................... 6

1.1 SCOPE ............................................................................................................................ 6

1.2 GLOSSARY OF TERMS ..................................................................................................... 6

1.3 SUMMARY OF CHANGES ............................................................................................... 8

2.0 INTRODUCTION TO POWER QUALITY ..................................................................... 9

2.1 TYPICAL POWER QUALITY PROBLEMS ........................................................................... 9

2.2 CAUSES AND EFFECTS OF POOR POWER QUALITY ...................................................... 10

3.0 VOLTAGE DEVIATIONS ......................................................................................... 11

3.1 VOLTAGE DEVIATIONS DURING NORMAL OPERATION ............................................... 11

3.2 VOLTAGE DIP DURING MOTOR STARTING .................................................................. 11

3.3 VOLTAGE DIP CAUSED BY NETWORK FAULTS ............................................................. 11

3.4 AUTOMATIC TRANSFER SYSTEM ................................................................................. 12

3.5 SYSTEM STABILITY STUDIES ......................................................................................... 13

3.6 MOTOR RE-ACCELERATION ......................................................................................... 13

3.7 SPECIFIC REQUIREMENTS FOR PLANT EQUIPMENT .................................................... 14

3.8 VOLTAGE DIP MITIGATION FOR MOTORS ................................................................... 14

3.9 VOLTAGE DIP MITIGATION FOR VARIABLE SPEED DRIVES (VSD OR VFD) ................... 15

3.10 VOLTAGE SURGE OR SPIKE .......................................................................................... 16

4.0 POWER FACTOR .................................................................................................. 17

4.1 POWER FACTOR CORRECTION ..................................................................................... 17

5.0 HARMONICS ........................................................................................................ 18

6.0 POWER QUALITY MEASUREMENT ........................................................................ 19

7.0 FREQUENCY DEVIATIONS ..................................................................................... 20

7.1 LOAD SHEDDING .......................................................................................................... 20

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8.0 PROTECTIVE RELAYS ............................................................................................ 21

8.1 TESTING ....................................................................................................................... 21

8.2 PROTECTION OF GRID INTERCONNECTION ................................................................. 21

9.0 BIBLIOGRAPHY .................................................................................................... 22

APPENDIX 1: TYPICAL STATISTICS OF POWER QUALITY DISTURBANCES ........................... 25

APPENDIX 2: IEC 61000-4-34 (CLASS 3) CURVE ................................................................. 26

APPENDIX 3: COIL HOLD-IN DEVICE ................................................................................. 27

APPENDIX 4: DIP-PROOF INVERTER ................................................................................. 28

APPENDIX 5: FERRO-RESONANT TRANSFORMER ............................................................. 29

APPENDIX 6: BOOST-REGULATOR FOR VFD ..................................................................... 30

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1.0 INTRODUCTION

1.1 SCOPE

1.1.1 This PTS gives recommended practices and requirements to attain and maintain power quality in PETRONAS facilities. It provides an overview of what are required to be done to mitigate typical power quality problems found in the plant or any facilities in PETRONAS. This PTS is developed based on lessons learnt, best practices and experiences.

1.2 GLOSSARY OF TERMS

1.2.1 General Definition of Terms & Abbreviations

Refer to PTS 00.01.03 for requirements, general terms & abbreviations.

1.2.2 Specific Definition of Terms

No Terms Description

1 Power Quality Ability to maintain (in AC circuit) a sinusoidal voltage and current at stipulated magnitude, frequency and continuity.

2 Disturbance in AC System. In AC system, disturbance or elements that can affect the quality of supply include among them (compare to nominal value):

i) Voltage deviations over, dip/sag, flicker, transient.

ii) Frequency high/low

iii) Harmonics voltage and current

iv) Resonance

v) Electro-magnetic interference

3 Electromagnetic Compatibility (EMC), 161-01-07, IEC 60050

The ability of a device, equipment or system to function satisfactorily in its electromagnetic environment without introducing intolerable electromagnetic disturbances to anything in that environment.

4 Frequency deviation, 604-01-06, IEC 60050

The difference between the system frequency at a given instant and the nominal

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value.

5 Harmonics Frequency components that are integer multiples of the fundamental line frequency.

6 Voltage deviation, 604-01-17, IEC 60050

That difference, generally expressed as a percentage, between the voltage at a given instant at a point in the system, and a reference voltage such as nominal voltage, a mean value of operating voltage, or declared supply voltage.

7 Voltage dip, 604-01-25, IEC 60050

A sudden reduction of the voltage at a given point in the system, followed by voltage recovery after a short period of time, from a few cycles to a few seconds.

8 Voltage surge, 604-03-14, IEC 60050

A transient voltage wave propagating along a line or a circuit and characterised by a rapid increase followed by a slower decrease of the voltage.

9 ATS

Automatic transfer system. Works by transferring power supply from one feeder or bus section to another as a result of a voltage dip of preset magnitude and duration.

10 PCC

Point of a power supply network where the plant power system is interconnected with the grid. This point is mutually agreed between the interconnected parties and is usually also the synchronizing point between the two systems.

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1.2.3 Abbreviations


1 ATS Automatic Transfer System

2 AVR Automatic Voltage Regulator

3 EMC Electromagnetic Compatibility

4 ENMC Electrical Network Monitoring and Control system

5 FAT Factory Acceptance Test

6 MCC Motor Control Center

7 OLTC On-Load Tap Changer

8 PCC Point of Common Coupling

9 PMS Power Monitoring System

10 PQ Power Quality

11 UPS Uninterruptible Power Supply

12 VSD Variable Speed Drive

13 VFD Variable Frequency Drive

1.3 SUMMARY OF CHANGES

This PTS 13.01.01 (G) replaces PTS 33.64.10.14 (January, 2011).

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2.0 INTRODUCTION TO POWER QUALITY

The impact of poor power quality on oil, gas and petrochemical inductries can be tremendous, running into millions of dollars on account of a single disturbance. These industries run many sensitive or mission-critical operations which when interrupted even momentarily, can take days to recover with the inevitable consequences of lost production opportunities, product loss due to flaring and perhaps more importantly, loss of reputation.

Examples of these populations are:

i) Continuous process operations driven by electric motors where a short voltage dip can cause motors to drop out thus interrupting the process. This is compounded by the fact that a large proportion of a plant load is made up of motors.

ii) Multi-stage batch operations where an interruption during one process can destoy the value of previous operations or result in off-spec products.

2.1 TYPICAL POWER QUALITY PROBLEMS

2.1.1 The chart in Appendix 1 shows the type of power quality problems that had caused plant upsets in sixteen plants with data taken from two surveys. Each survey collected data over a 21/2 year period.

2.1.2 From the surveys, the electrical disturbances encountered were:

i) Voltage dip ii) Relay mal-operation iii) Under-frequency iv) Poor power factor v) Harmonics vi) Electro-magnetic interference vii) Over-frequency

2.1.3 Relay mal-operation is not typically regarded as a power quality issue. However, it is seen to be a key contributor to equipment or power outages based on the surveys carried out.

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2.2 CAUSES AND EFFECTS OF POOR POWER QUALITY

2.2.1 The table below summarizes the impact poor power quality can have on plants.

Impact / Effects of poor power quality

Type Typical Cause Impact/Effects

Voltage dip Faults, switching of large loads e.g. motor starting

Motor drop-out, VSD trip, ATS transfer, motor stalling, generator trip, loss of synchronism

Voltage

swell

Switching transients, lightning Over-fluxing of transformers, insulation failure, generator trip

Voltage unbalance Asymmetric loads, unequal system

impedances

Loss of motor full load torque, overheating of rotor/stator and bearing damage. De-rating of cables, transformers

Under-frequency System

System overload due to loss of generation capacity (trip) to loss of

Load shedding, power swing to the grid, power blackout

Over-frequency

Loss of large loads, system faults Generator trip, power swing from the grid

Poor power factor

Large inductive load, lack or loss of power factor control.

Low power factor penalty, de-rating of equipment

Harmonics,

resonance

Non-linear loads, generator pitch windings, failure of harmonics filters, lack of detuning of PF correction capacitors

Overheating of equipment (e.g. transformers, motors, cables), overloading of neutral, maloperation of control systems, data network congestion, nuisance tripping of protective devices, over-stressing of power factor correction capacitors, saturation of CT, telecommunication interference, flickering screens or lights

Electro-

magnetic

interference

Lightning, high voltage switching, non-EMC compliant equipment, lack of shielding, bonding and earthing

Mal-operation or trip of equipment or protective devices

Table 1: Impact/ Effects of poor quality

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3.0 VOLTAGE DEVIATIONS

3.1 VOLTAGE DEVIATIONS DURING NORMAL OPERATION

3.1.1 During normal operation of a plant, the steady state voltage at the main intake bus, generator terminals and consumer terminals should not deviate by more than +/- 5% from nominal or rated value. Notwithstanding the above, the limits set by the Public Utility on voltage deviations caused by consumers at the PCC shall be adhered to.

3.1.2 Where the plant is connected to the utility grid, the interconnection transformer shall have an on-load tap changer which is normally on automatic control. Where the plant has an ENMC or PMS (Power Management System) to control the interchange of reactive power with the grid, the OLTC control shal be integrated with the power interchange control and local voltage control.

3.2 VOLTAGE DIP DURING MOTOR STARTING

3.2.1 Any voltage deviation of more than 10% below nominal voltage for duration of 10 ms to 60 seconds is considered a voltage dip. During motor starting, the voltage dip should not be more than -10% at the switchboard to which the motor is connected or more than +10% / -20% at motor terminals. Duration of such voltage dips may range from one second to several seconds. A motor starting study shal be performed during the Engineering stage of a project to confirm that these deviation limits are not exceeded. Where the study show that the deviation limits will be exceeded, measures (to be approved by the Principal) shall be taken to overcome the excessive voltage drop. The dynamic characteristics of the motor and the driven equipment shall be modeled in the study. Starters to reduce starting current should only be used if direct-on-line (DOL) start of motors will cause voltage dips exceeding the limits set above.

3.3 VOLTAGE DIP CAUSED BY NETWORK FAULTS

3.3.1 The severity of a voltage dip depends on the magnitude of the dip as well as the duration. Voltage dips caused by network fault typically last less than one second depending on the time taken by protection to clear the fault. The magnitude of the dip can be as much as 100% i.e. 0V at the point of fault, neglecting any fault impedance. The voltage dip experienced by other parts of the network differs according to network topology. The severity of the dip can cause plant interruptions e.g. motors to drop out or ATS to operate

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3.4 AUTOMATIC TRANSFER SYSTEM

3.4.1 Auto transfer systems (ATS) are usually implemented using under-voltage schemes. ATS under-voltage settings shall be coordinated with voltage dip statistics to minimize unnecessary ATS operation. ATS systems are inherently break-before-make systems which can cause momentary voltage loss to downstream equipment. As a minimum, the following is required for ATS systems:-

i) ATS schemes at different voltage levels shall be coordinated such that those for higher voltages switchboards (upstream) shall operate first thus preventing the lower voltages switchboards (downstream) ATS from operating.Relay mal-operation

ii) ATS undervoltage settings shall be such that nuisance operation is minimised for voltage dips.Poor power factor

iii) The trip of an incomer (circuit breaker open) due to relay or manual operation shall immediate initiate the ATS operation without waiting for the undervoltage relay to operate.

iv) When either incomers or feeders experience under-voltage at the same time, the ATS operation shall be blocked.

v) The operation of busbar protection or switchboard high set over-current protection on one section of a switchboard shall block the ATS operation. This is to prevent the healthy section of the switchboard from closing onto the faulted section.

vi) ATS shall be modeled in system studies including motor re-acceleration to ensure robustness of the overall system.

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3.5 SYSTEM STABILITY STUDIES

3.5.1 Transient stability studies shall be carried out for plants or projects which have synchronous generators or motor-reacceleration schemes. Attention shall be paid to the critical clearance time of faults to prevent generator pole slipping or to ensure motor re-acceleration is successful. Reference is made to PTS 13.00.02 Section 6.2.3. The CCT shall be determined for both internal plant faults and external grid faults.

3.5.2 In addition to fast fault clearance as determined by CCT, pole slipping protection (out-of-step relay) may be considered for generators and interconnection with the grid. The out-of-step relays shall be coordinated with generator loss-of-field (LOF) relays since the LOF relays may also operate during pole slipping conditions.

3.6 MOTOR RE-ACCELERATION

3.6.1 A motor re-acceleration scheme shall be implemented to restart motors after a voltage dip. This will require motor re-acceleration studies to be carried out. Fault clearance times shall be determined to allow successful re-acceleration.

3.6.2 Process requirements or constraints during motor restart shall be taken into consideration. Voltage at switchboards busbars shall be maintained at minimum 90% during motor re-acceleration. Motors shall be equipped with restarting facility as required by the Principal. For system studies modeling, the actual contactor drop-out voltages shall be used which must be supported by factory tests. In the absence of such tests, a value of 65% nominal voltage may be assumed for contactor drop-out.

3.6.3 Motor restart schemes shall be implemented as follows:

On motor drop-out, if the voltage recovers to 90% nominal in:

i) less than 0.2 seconds, immediate restart of all motors

ii) between 0.2 4 seconds, sequential restart

iii) more than 4 seconds, no restart

3.6.4 Motors controlled by circuit breakers or motors controlled by external supplies from UPS shall be equipped with under-voltage relays and restart relays to trip the motors. This is to prevent motors from stalling which can restrain voltage recovery or subject the motor to overcurrent during under-voltage condition. Under-voltage relays shall be inherently selfresetting to allow automatic restart.

3.6.5 For sequential restart, motors shall be restarted in batches based on criticality or process requirements. Attention shall be given to start permissive signals originating from process instrumented systems.

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3.7 SPECIFIC REQUIREMENTS FOR PLANT EQUIPMENT

3.7.1 Plant equipment shall have voltage dip immunity characteristics in accordance with IEC 61000-4-11, 61000-4-34 and 61000-2-4. Reference is made to PTS 13.00.02 Section 3.7.2.

3.7.2 In particular, specifications for motor contactors shall highlight this requirement and tests shall be conducted at factory to ascertain compliance.

3.7.3 For plants equipped with generators, dynamic response tests shall be carried out to fine-tune the governor and excitation systems for proper dynamic behaviour (refer PTS 13.00.02 Sections 7.3 and 7.4 and PTS 13.02.01 Section 4.3.1.3.4). This should be done during FAT or commissioning.

3.7.4 Emergency diesel generators are designed to start up automatically and supply power to plant vital loads in the event of voltage loss / dips. This function shall be tested on a regular basis as part of plant routine testing of equipment (auto start test). It shall also be part of the testing regiment to load the machines either by synchronising them to the plant electrical system/grid or using a load bank. For new installations, the design of the emergency switchboard shall allow auto-start functional test (break-before-make) to be carried out without causing any voltage dip to the essential loads.

3.8 VOLTAGE DIP MITIGATION FOR MOTORS

3.8.1 Since motor contactors will inherently drop out if the voltage dip is severe enough, a successful motor re-acceleration scheme is vital to avoid or minimize interruption to plant operation. In general, plant equipment should comply with the voltage dip immunity characteristics as per IEC 61000-4-34 (Appendix 2).

3.8.2 There are equipment available (e.g. dynamic voltage restorer, static compensator) which can boost system reactive power during voltage dips to maintain system voltages but they usually involve prohibitive costs. A more pragmatic approach is to maintain motor control voltage during voltage dips to prevent the contactors from dropping out.

3.8.3 Motors with control circuit power supply from UPS will not drop out during voltage dips. However, to prevent these motors from stalling, under-voltage protection shall be provided.

3.8.4 To eliminate the risk of critical motors not restarting successfully, the following two measures can be implemented to improve the immunity of these motors during voltage dips. The behaviour of such voltage dip mitigation devices need to be modeled and included in the transient stability and motor re-acceleration studies.

i) Coil hold-in device

The hold-in device is connected between the power source and the contactor coil (Appendix 3). During voltage dips, sufficient current flow is maintained through the contactor coil to hold the main contacts in place. The circuit shall be designed to provide hold-in current for dips down to about 25% remaining voltage.

ii) Dip-proof inverter a) The dip-proof inverter consists of a static switch in series with, and an inverter in

parallel to, the load. Energy is stored in a capacitor bank (Appendix 4). During

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standby operation, the static switch supplies power directly to the load, the inverter is switched off and the capacitors are charged to the full operating voltage. Should there be a deviation which is greater than a preset value, the static switch is switched off and the inverter is activated. Switchover is typically less than 0.2 ms.

b) If the voltage recovers within a preset time, the inverter supply is synchronized to the mains and the load is switched back to the supply, the capacitors are recharged in less than one second and the inverter is ready to compensate for the next voltage dip. If the input voltage does not recover within the preset time, the load is switched back to the supply regardless of the voltage level.

iii) Ferro-resonant transformer a) Also known as constant voltage transformer (CVT), it works by saturating the core

with magnetic flux thus maintaining a relatively constant output voltage during input voltage variations. The ability of the CVT to regulate its output voltage depends on the loading of the CVT. A higher loading will decrease the input range over which it can regulate its output voltage (refer Appendix 5).

b) The inrush current due to switching on of loads (e.g. contactor coils, PLC) connected to the CVT has to be considered when sizing the CVT. This is to ensure there is no excessive control voltage dip when the loads are switched on. For each CVT, the largest inrush load shall be considered. Inrush currents of motor contactor coils which are set to energize simultaneously as part of a motor re-acceleration scheme,shall be summed up as one combined inrush load.

c) Operation in the saturated region produces an undesirable effect i.e. harmonics or sinewave distortion. Therefore most ferro-resonant transformers incorporate an L-C circuit (tank circuit) to filter out most of the harmonics.

3.9 VOLTAGE DIP MITIGATION FOR VARIABLE SPEED DRIVES (VSD OR VFD)

3.9.1 Variable speed drives are becoming an integral part of plants due to their energy saving potential. However, one of the main disadvantages of VSD is its susceptibility to voltage dip. The following are some measures which should be considered to improve the immunity of VSD to voltage dip.

i) Reducing the trip level and/or increasing the time delay of VSD

VSDs are typically programmed by the manufacturer to trip instantly for a voltage dip of about 80 - 90% of nominal. This sensitive trip setting is usually selected by the manufacturer to protect the electronic components of the VSD. However, in many cases, there is room for relaxing this trip level or introducing time delays into the trip sequence without sacrificing the VSD integrity. This level of parameter change may require the manufacturer to provide access to the factory level parameters, which generally cannot be changed by the customer.

ii) Ride-through using flying restart

The ability of a VSD to start into a spinning motor without tripping on an overcurrent fault somewhere in the network, is known as Flying Restart capability. In this method, when the voltage dip causes the VSD to reach its undervoltage trip level, the drive will shut off the inverter section and thus remove power from the motor instead of tripping.

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The motor will coast down during the duration of the dip and as soon as the voltage recovers, the VSD will start into the still-spinning motor and ramp up to set speed.

iii) Ride-through using load inertia

This option which is provided by some manufacturers of VSDs, uses the energy stored in the mechanical load to keep the DC bus voltage of the VSD from dropping down to the trip level. This is accomplished by running the inverter section during a voltage dip at a frequency slightly below the motor frequency, causing the motor to act as a generator. Similar to the flying restart option, the motor speed will drop while it is acting as a generator. However, the advantage is that the motor is never disconnected from the drive. This option works best for those high-inertia loads that are allowed to slow down without interrupting the process.

iv) Ride-through using boost regulator a) A Boost Regulator can be used to provide ride-through to VSDs during undervoltage

condition. Essentially, a boost converter uses the voltage remaining on the AC line during an undervoltage condition and the remaining available energy to maintain the DC bus voltage above the trip level. Appendix 6 shows the diagram of a commercially available voltage sag ride-through device using the boost regulator topology. The unit converts the incoming AC voltage to DC using a rectifier, and then uses one or more inductive chopper sections to boost the DC bus voltage during a voltage sag and thus maintain its voltage above the trip level.

b) Ride-through capability for deeper dips can be provided by using energy storage options, such as battery or capacitors, with the boost regulator.

3.10 VOLTAGE SURGE OR SPIKE

3.10.1 The main causes of voltage surges or spikes are lightning and high voltage switching. When required, surge arrestors are used to protect against the effects of overvoltages. However, the surge arrestor will offer optimized protection level only if it is installed directly across the terminals of the equipment to be protected. In practice, it is not always possible to locate the arrestor close to electrical equipment like transformers, generators or motors and an inevitable separation distance will be required.

3.10.2 Protection against switching overvoltages is normally not a problem for most applications since travelling wave effects can be neglected on short distances. For fast transient overvoltages like lightning, conductor inductance and travelling wave effects can cause significant voltage differences between the arrestor and the equipment.

3.10.3 Calculation of separation distances can be found in IEEE Standard C62.22-19 whereas calculation of arrestor protective zones is described in IEC 60071-2.

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4.0 POWER FACTOR

4.1 POWER FACTOR CORRECTION

4.1.1 Power factor is the ratio of active power and apparent power in an AC system. Fundamental power factor is the value measured without considerations of harmonics distortion while true power factor is a value that includes both fundamental and harmonics distortions.

4.1.2 True power factor can be measured with equipment that measure true RMS values. Low true power factor means higher losses in the system. Low true power factor can be improved by reducing the harmonics level in the system.

4.1.3 The power factor measured by Utilities companies is the fundamental value. Power factor at the point of common coupling (PCC) should be maintained at a value to avoid financial penalty. Control of power factor may be affected by the following methods in order of preference (refer PTS 13.00.01 Section 4.4):-

(i) Variation of excitation of synchronous machines (generators and motors).

(ii) Static capacitors at individual HV motors

(iii) Static capacitor banks connected to distribution switchboards and MCCs.

4.1.4 The correction of power factor at other branches in a network depends on the economic benefit. Where capacitors are used, measurements and / or harmonic studies shall be carried out to verify that they do not cause any resonance effects in the system. If necessary, the capacitors shall be de-tuned accordingly by adding a reactor in series.

4.1.5 Capacitor banks may be connected in star or delta up to a rating of 1000kVA above which, the connection shall be double-star. The star point shall not be earthed. For double-star connection, unbalance protection shall be provided to monitor the star point voltages or differential protection shall be provided across the two halves of the capacitor banks.

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5.0 HARMONICS

5.1 HARMONICS LEVELS

5.1.1 Harmonics levels shall comply with PTS 13.00.01. However, if the Utility imposes more stringent requirements, then those limits shall apply as shown in the table below.

5.1.2 Reference is to be made to IEEE 519 for allowable harmonic current levels. Harmonics generated in static UPS, VSD and power electronics devices shall comply with the EMC requirements as specified in:

(i) PTS 13.12.02 Static DC UPS units

(ii) PTS 13.12.01 Static AC UPS units

(iii) PTS 13.22.01 A.C Electrical Variable Speed Drive Systems

(iv) PTS 13.13.03 Electrical Process Heaters

5.1.3 Required FAT tests shall be carried out to ensure compliance with above limits. Where FATs are not possible for distribution systems, equipment shall be specified to IEC61000-3-2, software simulations performed to gauge IEEE519 compliance, and results verified at site.

5.2 MITIGATION OF HARMONICS

5.2.1 A harmonics study shall be carried out for plants or projects which have sizeable power capacitors or power electronics equipment. In addition, power quality measurements shall be carried out in existing plants to ascertain the level of harmonics in a facility.

5.2.2 To mitigate excessive harmonics, harmonic filters shall be installed. The type of filter to be installed should be decided based on effectiveness, reliability and economic considerations. There are generally two types of filters; passive and active filters. Where passive filters consisting of LC elements are installed, they should be of the acceptor circuit type (L and C in series). The filters shall be connected in parallel with the supply.

5.2.3 Active harmonic filters shall be connected in parallel with the supply. In general, they shall be connected as close as possible to the harmonic source.

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6.0 POWER QUALITY MEASUREMENT

6.1 GENERAL

6.1.1 Permanently installed PQ cum disturbance recorder should be installed at each Point of Common Coupling with the grid. As a minimum, plant switchboards shall have facilities for plug-in measurement of 3-phase voltage and current by a portable PQ analyzer.

6.1.2 Portable PQ measuring instruments are recommended for quick snapshots of power quality at the point of measurement. Plant personnel should be trained to use them and to analyze the results.

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7.0 FREQUENCY DEVIATIONS

7.1 LOAD SHEDDING

7.1.1 During normal operation, frequency shall be maintained at 50 Hz +/- 2% as per PTS 13.00.01 Section 3.

7.1.2 For plants which are connected to the grid, the system frequency will be determined by the grid. Plants with their own generation and can run on island mode shall have a load shedding scheme (PTS 13.30.01 Section 4). Dynamic studies for load shedding schemes shall be carried out accordingly.

7.1.3 During island operation, plants that run N+ 1 generator normally allow for the trip of the largest generator without causing any impact to the plant. In such a trip scenario, the dynamic response of the remaining N generators shall be such that the system frequency will not drop to a value that initiates load shedding. The prime mover dynamic characteristics shall be fine-tuned by testing in accordance with PTS 13.00.02 Section 7 and PTS 13.02.01 Section 4.

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8.0 PROTECTIVE RELAYS

8.1 TESTING

8.1.1 To prevent wrong settings, protective relay settings shall be managed in a proper manner and any changes made shall be auditable. Relay testing shall be carried out in accordance with PTS 13.02.01 Section 4.5.

8.1.2 Directional relays shall be system tested to ensure that the direction of protection have been set correctly. This is done by reversing the normal current flow direction until the relays pickup. Generator reverse power relay shall be tested by decreasing the governor setting. Loss-of-field relay shall be tested by decreasing the AVR setting at minimum load. Directional over-current relays shall be tested by temporarily reducing the setting to a practical value and reversing the current flow.

8.1.3 Reverse power protection for grid interconnection shall be tested by exporting power to the grid. The setting may be reduced for the purpose of the test.

8.1.4 The use of a database system to manage relay settings is recommended.

8.2 PROTECTION OF GRID INTERCONNECTION

8.2.1 As a minimum, the following protection shall be applied for the grid interconnection.

i) transformer protection (over temperature, buchholtz, pressure) ii) cable pilot wire (from grid CB to transformer) iii) transformer differential iv) restricted earth fault v) over-current and earth fault vi) directional over-current vii) reverse power viii) under-voltage ix) under-frequency x) syn-check

8.2.2 The settings for the non-unit protection (directional over-current, reverse power, under-voltage, under-frequency) shall be selected based on system studies with relevant input from the grid.

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9.0 BIBLIOGRAPHY

In this PTS, reference is made to the following other Standards/Publication. Unless specifically designated by date, the latest edition of each publication shall be used, together with any supplements/revisions thereto:

PETRONAS TECHNICAL STANDARDS

Index to PTS PTS 00.01.01

PTS Requirements, general terms & abbreviations PTS 00.01.03

Electrical Engineering Guidelines PTS 13.00.01

Electrical Network Monitoring and Control System - Application

PTS 13.30.01

Electrical Supply and Generation design and operation PTS 13.00.02

Electromagnetic Compatibility (EMC) requirements PTS 13.50.01

Synchronous A.C. Machine PTS 13.21.01

Packaged Unit A.C. Generator Sets PTS 13.21.02

Static D.C. Uninterruptible Power Supply (DC UPS) units PTS 13.12.02

Static A.C. Uninterruptible Power Supply unit (static AC UPS) PTS 13.12.01

A.C. Electrical Variable Speed Drive Systems PTS 13.22.01

Low-voltage Switchgear and Controlgear Assemblies PTS 13.11.02

High-voltage Switchgear and Controlgear Assemblies PTS 13.11.01

Electrical Process Heaters PTS 13.13.03

Field Commissioning and Maintenance of Electrical Installations and Equipment

PTS 13.02.01

Electrical Engineering Guidelines PTS 13.00.01

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Electrical Network Monitoring and Control System - Application

PTS 13.30.01

Electrical Supply and Generation design and operation PTS 13.00.02

Electromagnetic Compatibility (EMC) requirements PTS 13.50.01

Synchronous A.C. Machine PTS 13.21.01

Packaged Unit A.C. Generator Sets PTS 13.21.02

Static D.C. Uninterruptible Power Supply (DC UPS) units PTS 13.12.02

Static A.C. Uninterruptible Power Supply unit (static AC UPS) PTS 13.12.01

A.C. Electrical Variable Speed Drive Systems PTS 13.22.01

Low-voltage Switchgear and Controlgear Assemblies PTS 13.11.02

High-voltage Switchgear and Controlgear Assemblies PTS 13.11.01

Electrical Process Heaters PTS 13.13.03

Field Commissioning and Maintenance of Electrical Installations and Equipment

PTS 13.02.01

AMERICAN STANDARDS

Recommended Practice and Requirements for Harmonic Control in Electrical Power Systems

IEEE 519

OTHER STANDARDS

Electromagnetic Compatibility (EMC) IEC 61000

Compatibility levels in industrial plants for low-frequency conducted disturbances

IEC 61000-2-4

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Voltage dips/interruptions/variation immunity IEC 61000-4-11

Testing and measurement techniques voltage dips, short interruptions and voltage variations immunity tests for equipment with input current more than 16A per phase

IEC 61000-4-34

Specification for Semiconductor Processing Equipment Voltage Sag Immunity

SEMI F-47

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APPENDIX 1: TYPICAL STATISTICS OF POWER QUALITY DISTURBANCES

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APPENDIX 2: IEC 61000-4-34 (CLASS 3) CURVE

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APPENDIX 3: COIL HOLD-IN DEVICE

Before installation

After installation

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APPENDIX 4: DIP-PROOF INVERTER

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APPENDIX 5: FERRO-RESONANT TRANSFORMER

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APPENDIX 6: BOOST-REGULATOR FOR VFD

Documents

130101 Power Quality