Generator Protection Master Abb (elaborate)

Generator Protection

Sept 2004

Generator Protection

The extent and types of protection specified will depend on the following factors :-

Type of prime mover and generator construction MW and voltage ratings Mode of operation Method of connection to the power system Method of earthing

2

2

Connection to the

Power System

1. Direct :

2. Via Transformer :

3

3

Typical Generator Installations

Generator Transformer

Generator Transformer Station Transformer

Earthing Transformer

Unit / Station Transformer

1(b) 4

Unit Transformer

1(c) 4

Generator Protection Requirements

To detect faults on the generator To protection generator from the effects of abnormal power system operating conditions To isolate generator from system faults not cleared remotely

Action required depends upon the nature of the fault.

Usual to segregate protection functions into :

Š Urgent Š Non-urgent Š Alarm 5

5

Generator Faults Mixture of mechanical and electrical problems. Faults include :Insulation Failure

Š Stator Š Rotor Excitation system failure Prime mover / governor failure Bearing Failure Excessive vibration Low steam pressure etc.

6

6

System Conditions

Short circuits Overloads Loss of load Unbalanced load Loss of synchronism

7

7

Generator Protections to be Considered Earth faults on stator and generator connections Phase faults on stator and generator connections Interturn faults on stator Backup protection :- External Earth faults External Phase faults Failure of prime mover Loss of field Unbalanced loading Rotor earth faults and interturn faults Overload Failure of speed governing system Sudden loss of load

8

8

Stator Earth Fault Protection

Fault caused by failure of stator winding insulation Leads to

burning of machine core welding of laminations

Rebuilding of machine core can be a very expensive process Earth fault protection is therefore a principal feature of any generator protection package TYPE OF PROTECTION

9

Î

METHOD OF EARTHING

Î METHOD OF CONNECTION 9

Method of Earthing (1)

10

z

Machine stator windings are surrounded by a mass of earthed metal

z

Most probable result of stator winding insulation failure is a phase-earth fault

z

Desirable to earth neutral point of generator to prevent dangerous transient overvoltages during arcing earth faults

z

Several methods of earthing are in use

z

Damage resulting from a stator earth fault will depend upon the earthing arrangement

10

Method of Earthing (2)

Solidly Earthed Machines :

Fault current is high Rapid damage occurs

Š Š

burning of core iron welding of laminations

Used on LV machines only

11

11

Method of Earthing (3) Desirable to limit earth fault current : limits damage reduces possibility of developing into phase-phase fault Degree to which fault current is limited must take into account : detection of earth faults as near as possible to the point ease of discrimination with system earth fault protection (directly connected machines)

12

neutral

12

Method of Earthing : Limitation of Earth Fault Current (1) Less than 5A :

F

Earth faults on the power system are not seen by the generator earth fault protection.

Discrimination not required ∴ can limit current to very low value. 20A : Used on oil and gas platforms. Limits power supply disturbance, but still enables grading of up to 3 zones.

13

13

Method of Earthing : Limitation of Earth Fault Current (2)

100A : As for 20A, but higher current allows better discrimination and sensitivity. Generator Full Load Current (1200A max) : Most popular. Used for ease of fault detection and discrimination. Residual connection of CTs can be used, BUT Can result in serious core damage.

14

14

Stator Earth Fault Protection and Protection Against Earth Faults on Generator Connections Depending on the Generator arrangement this can be provided by :Time delayed overcurrent protection Time delayed earth fault protection Sensitive earth fault protection Neutral displacement voltage relay Neutral displacement voltage detection by overcurrent relay High impedance restricted earth fault protection High impedance differential protection Biased differential protection Directional earth fault protection 100% stator earth fault protection

15

15

Overcurrent Protection (1) For small generators this may be the only protection applied. With solid earthing it will provide some protection against earth faults. For a single generator, CTs must be connected to neutral end of stator winding.

51 16

16

Overcurrent Protection (2) For parallel generators, CTs can be located on line side.

51

17

17

Stator Earth Fault Protection Directly Connected Generators :

51N

Earthed Generator : Earth fault relay must be time delayed for co-ordination with other earth fault protection on the power system.

50N

51N

Unearthed Generators : Other generators connected in parallel will generally be unearthed. Protection is restricted to faults on the generator, grading with power system earth fault protection is not required. A high impedance instantaneous relay can be used (Balanced Earth Fault protection). 18

18

Percentage Winding Protected 11.5kV; 75,000KVA

xV

250/1A

IS

xV R For operation

ΙF =

Ι S(PRIMARY) R

33Ω

< ΙF

xV R x.6600 < < x.200 33 1 Ι S(SECONDARY) < x.200 x < 0.8x 250 <

∴ For protection of 90% of winding; x = 1-0.9 = 0.1 Relay setting = 0.8 x 0.1 = 0.08A = 8% of 1A 19

19

Stator Earth Fault Protection (1) Generators connected via step-up transformer (resistance earthed) :

51N

50N

Instantaneous protection (50N) : System earth faults ARE not seen by generator earth fault protection ∴ instantaneous relay may be used. Set to 10% of resistor rating (avoids operation due to transient surges passed through generator transformer interwinding capacitance). Advantage : Fast

20

20

Stator Earth Fault Protection (2)

Time delayed protection (51N) : Time delay prevents operation on transient surges. A more sensitive current setting may be used. Set to 5% of resistor rating. Advantage : Sensitive On large machines considered worthwhile to use both instantaneous and time delayed. 21

21

Stator E/F Protection for Generator with High Resistance Earthing via Distribution Transformer (1) Transformer / Resistor Rating ~ 30 Secs.

Generator

Distribution Transformer Turns Ration = N

R

51N

59

Overvoltage Relay With 3rd Harmonic Rejection

* Set > 3RD harmonic current * Or use relay with 3RD harmonic rejection

R’ = Effective Primary Resistance = N2.R 22

22

Stator E/F Protection for Generator with High Resistance Earthing via Distribution Transformer (2) To avoid overvoltages :R’ > Total 3Ø capacitive reactance ¾ 106 ohms 6πf C To avoid Ferroresonance Earthing transformer must not saturate Due to :-

Sudden loss of load Field forcing Flux doubling due to point on wave swtiching

∴ Primary knee point voltage is VØ/Ø ⇒ 1.3 VØ/Ø 23

23

Restricted Earthfault Protection

RSTA B

High Impedance Principle

64

Instantaneous Protection Protects approx. 90 - 95% of generator winding. All CT’s should be similar - Good quality - Class ‘X’ 24

24

Restricted Earthfault Protection for Generators on 4 Wire L.V. Systems (1) Earthing at Generator Neutral

5 x CT’s required RSTAB 64

25

25

Restricted Earthfault Protection for Generators on 4 Wire L.V. Systems (2) Earthing at Busbars

RSTAB 64 4 x CT’s required

26

26

Differential Protection (1) Provides high speed protection for all fault types May be : High impedance type : Biased (low impedance) type Good quality CT’s required CT’s required in neutral end of winding

High Impedance Scheme

Stabilising Resistors Relay

27

27

Differential Protection (2)

BIAS

BIAS

OPERATE

Biased Differential Scheme 28

28

Differential Protection (3)

INTERPOSING C.T.

Overall Differential Scheme 29

29

Stator Earth Fault Protection

100% Stator Earth Fault Protection : Standard relays only cover 95% of winding. Probability of fault occuring in end 5% is low. On large machines 100% stator earth fault protection may be required. Two methods :

30

*

Low Frequency Injection

*

Third Harmonic Voltage Measurement 30

100% Stator Earth Fault Protection For Large Machines Only Two methods :z Low frequency injection

z Third harmonic voltage - various

Low Frequency Injection

Earthing Transformer

59 Complete protection during start-up if source is independent of generator, e.g. derived from station battery.

Injection Transformer

Independent of system V, f and load current. High cost due to injection equipment.

51

31

Alternative Injection Points 31

Third Harmonic Neutral Voltage Scheme

Relies on >1% generated 3rd harmonic volts 59

27 59P

27 - 3rd harmonic undervoltage relay. 59P - Terminal Voltage Check

59

Allows trip if circuit breaker is open but terminal voltage present.

59P

TRIP 59 - Conventional neutral overvoltage protection.

27

OVERLAP

27

59 FUNDAMENTAL FREQ. ELEMENT

0

50

100

Earth Fault Position 32

32

Stator Phase-Phase Fault Protection (1)

Phase-phase faults caused by :

z

Insulation failure

z

Flashover in terminal box

Majority of phase-phase faults begin as earth faults. High fault current causes rapid damage ∴ fast protection required.

33

33

Stator Phase-Phase Fault Protection (2) Single Generator Use time delayed overcurrent. CTs must be in neutral side to cover winding faults.

51

51

51

Small solidly earthed machines - overcurrent also provides degree of earth fault protection. Overcurrent is often only protection applied to small machines. 34

34

Stator Phase-Phase Fault Protection (3) Larger Machines, Parallel Operation Require Differential Protection

Type types :

z

High impedance - most common

z

Biased (low impedance) - used for generator - generator transformer sets

Class X CTs required.

35

35

Stator Phase-Phase Fault Protection (4) High Impedance Scheme

Stabilising Resistors Relay

36

36

Stator Phase-Phase Fault Protection

z Previous methods require access to winding neutral end

z Small machines : z

Star connection made inside machine

z

Winding neutral ends are not brought out

z If high speed protection required, restricted earth fault scheme should be used

37

37

Stator Interturn Fault Protection (1)

z Longitudinal differential system does not detect interturn faults z Interturn fault protection not commonly provided because : z

Fault rare

z

Even if interturn fault occurs, will develop into earth fault

z Possible that serious damage can occur before fault is detected

38

38

Stator Interturn Fault Protection (2) Zero Sequence Voltage Method :

VA VB VC FAUL T

VA

VB VC

VR

3rd Harmonic Rejection Required

R

39

VR = VA + VB + VC 39

Stator Interturn Fault Protection (3) Transverse Differential Protection (Double Wound Machines) :

Bias Coils

Operate Coils

40

40

Prime Mover Failure (1) Isolated Generators : Machine slows down and stops. Other protection initiates shut down.

Parallel Sets : System supplies power - generator operates as a motor. Seriousness depends on type of drive.

Steam Turbine Sets : Steam acts as a coolant. Loss of steam causes overheating. Turbulence in trapped steam causes distortion of turbine blades. Motoring power 0.5% to 6% rated. Condensing turbines, rate of heating slow. Loss of steam instantly recognised.

41

41

Prime Mover Failure (2) Diesel Driven Sets : Prime mover failure due to mechanical fault. Serious mechanical damage if allowed to persist. Motoring power from 35% rated for stiff machine, to 5% rated for run in machine.

Gas Turbines : Motoring power 100% rated for single shaft machine, 10% to 15% rated for double shaft.

Hydro Sets : Mechanical precautions taken if water level drops. Low head types - erosion and cavitation of runner can occur. Additional protection may be required.

42

42

Prime Mover Failure (3)

Reverse Power Protection : Reverse power measuring relays used where protection required. Single phase relay is sufficient as prime mover failure results in balanced conditions. Sensitive settings required - metering class CTs required for accuracy.

43

43

Reverse Power Protection (1) Importing lagging VAR’s -MVARLAG

Leading P.F. Operate -MW

Restrain +MW

87.1°

Operate

Restrain Lagging P.F.

+MVARLAG Exporting lagging VAR’s 44

44

Loss of Excitation (1) EFFECTS Single Generator : Loses output volts and therefore load. Parallel Generators : Operate as induction motor (> synch speed) Flux provided by reactive stator current drawn from system-leading pf Slip frequency current induced in rotor - abnormal heating Situation does not require immediate tripping, however, large machines have short thermal time constants - should be unloaded in a few seconds.

45

45

Loss of Excitation (2) Simple Protection Scheme

Field Winding

Exciter

Shunt

Requires access to

Ie

field connections. DC relay (setting < Ie min)

Not suitable if generator operates normally with low

Aux Supply

excitation (large T1

machines). Alternative scheme monitors impedance

T2

Overcomes Slip Frequency Effects

0.2 - 1 sec

at generator Alarm or terminals. Trip

2 - 10 secs 46

46

Loss of Excitation (3) Alternative Scheme

XG

XT

XS ES

EG R

On field failure ratio EG / ES decreases and rotor angle increases.

Machine starts to pole slip with decaying internal EMF.

47

47

Loss of Excitation (4) Impedance seen by relay follows locus shown below :

X

Load Impedance

Impedance Locus

R Offset – Prevents operation on pole slips Diameter

Typically : Offset 50-75%X’d Diameter 50-100% XS 48

Relay Characteristic Time Delayed 48

Impedance Diagram for Various Operating Modes of Machine jx

EXPORT WATTS EXPORT VARAG

IMPORT WATTS EXPORT VARLAG

R

-R EXPORT WATTS EXPORT VARLEAD

IMPORT WATTS EXPORT VARLEAD

-jx

49

EXPORTING VARLAG

=

IMPORTING VARLEAD

EXPORTING VARLEAD

=

IMPORTING VARLAG 49

Impedance Locus of Generator Operating Out of Synchronism +jX

EG/ES = 1.5 2.0 LOAD POINT

5.0 5 A EG/ES = 1 G

0.2

0.5

0.7

-jX 50

50

Rotor and Power Factor Angles Relay Location I

Xd

E

V

E IX d

V

σ Ø

= =

Rotor Angle Power Factor Angle

I

σ Ø 51

51

Power Limit Impedance Diagram jx

Z

Ø

V2/C R

52

VΙ.COS ∅ = C Ι C COS ∅ = V V2 V2 Z = COS ∅ C

52

Loci of Constant Rotor Angle σ jx

R

Xd

53

120°

90°

σ= 30°

53

Relay Characteristic Req’d to Allow Generator Operation with Rotor Angles up to 'σ' jx Constant Power

Offset 0.75X’d

Diameter

R Limiting Generation Point Constant σ Relay Characteristic

54

54

Unbalanced Loading (1)

Effects

55

z

Gives rise to negative phase sequence (NPS) currents results in contra-rotating magnetic field.

z

Stator flux cuts rotor at twice synchronous speed.

z

Induces double frequency current in field system and rotor body.

z

Resulting eddy currents cause severe over heating.

55

Unbalanced Loading (2) Protection z

Machines are assigned NPS current withstand values : * *

56

Continuous NPS rating, I2R Short time NPS rating, I22t

z

If possible level of system unbalance approaches machin continuous withstand, protection is required.

z

Use negative sequence overcurrent relay.

z

Relay should have inverse time characteristic to match generator I22t withstand.

z

Relay pick-up setting should be just below I2R rating.

z

Can use an alarm setting of 70% to 100% to pick-up. 56

Unbalanced Loading (3) Machine NPS Withstand Values TYPE OF MACHINE

ROTOR COOLING

Typical Salient Pole Cylindrical Rotor

Conventional Air Conventional Hydrogen 0.5 PSI Conventional Hydrogen 15 PSI Conventional Hydrogen 30 PSI Direct Hydrogen 40 - 60 PSI

Cylindrical Rotor Cylindrical Rotor Cylindrical Rotor

57

I2R (PU CMR)

I22t = K

0.40

60

0.20

20

0.15

15

0.15

12

0.10

3

57

Rotor Earth Fault Protection (1)

Field circuit is an isolated DC system. z

Insulation failure at a single point : -

z

Insulation failure at a second point : -

z

58

No fault current, therefore no danger Increase change of second fault occurring

Shorts out part of field winding Heating (burning of conductor) Flux distortion causing violent vibration of rotor

Desirable to detect presence of first earth fault and give an alarm. 58

Rotor Earth Fault Protection (2) Potentiometer Method

Exciter

R

Required sensitivity approximately 5% exciter voltage. No auxiliary supply required. “Blind spot” - require manually operated push button to vary tapping point. 59

59

Rotor Earth Fault Protection (3) AC Injection Method

AC Auxiliary Supply R

Brushless Machines No access to rotor circuit Require special slip rings for measurement If slip rings not present, must use telemetering techniques (expensive) 60

60

Overload Protection (1) high load current Ð heating of stator and rotor Ð insulation failure Governor Setting Should prevent serious overload automatically. Generator may lost speed if required load not be met by other sources. High reactive power flow can give high stator current - not affected by governor settings.

61

61

Overload Protection (2) Direct Temperature Measuring Devices Resistance temperature detectors (RTDs), thermocouples etc., embedded in windings. Provide alarm and/or trip via auxiliary relays. Overcurrent Protection Set just above maximum load current. Intended for short circuit protection. Thermal Replica Relays Current operated. May have ambient temperature compensation.

62

62

Generator Back-Up Protection (1) Overcurrent Protection Typical use : Very or extremely inverse for LV machines Normal inverse for HV machines Must consider generator voltage decrement characteristic for close-in faults. With reliable AVR system, “conventional” overcurrent relays may be used. Otherwise, voltage controlled / restrained relays are required.

10 x FL

with AVR Full Load

no AVR Cycles

63

63

Generator Back-Up Protection (2) Overcurrent Protection Voltage Restrained Operating characteristic is continuously varied depending on measured volts. Alternatively, use impedance relay. Voltage Controlled Relay switches between fault characteristic and load characteristic depending on measured volts.

F 64

64

Voltage Controlled Overcurrent Protection

Fault Characteristic

I 65

Current Pick - up

t

Overload Characteristic

Is

Vs Voltage 65

Voltage Restrained Overcurrent Protection

Equivalent to impedance devices

Current Pick-up

More suited for indirect connected generators

I> KI>

VS2 VS1 Voltage 66

66

10 O/L CHARAC 1.0

FAULT CHARAC LARGEST OUTGOING FEEDER

t se c

GENERATO R DECREMEN T CURVE

0.1

0.01 100 67

240 600 1000

3000

10,000

6.6kV 5MVA 115% XS 500/5 200/5

AMPS 67

Impedance Relay jx

R

RELAY CHARACTERISTI C MZTU

Set to operate at 70% rated load impedance when voltage drops to zero, current required to operate relay is 10% rated current. Built-in timer for co-ordination purposes. 68

68

Under & Over Frequency Conditions (1)

Over Frequency Results from generator over speed caused by sudden loss of load. In isolated generators may be due to failure of speed governing system. Over speed protection may be provided by mechanical means. Desirable to have over frequency relay with more sensitive settings.

69

69

Under & Over Frequency Conditions (2) Under Frequency Results from loss of synchronous speed due to excessive overload. In isolated generators may be due to failure of speed governing system. Under frequency condition gives rise to:

Š Overfluxing of stator core at nominal volts Š Plant drives operating at lower speeds - can affect generator output

Š Mechanical resonant condition in turbines Desirable to supply an under frequency relay. Protection may be arranged to initiate load shedding as a first step.

70

70

Under & Over Voltage Conditions (1)

Protection Under & over voltage protection usually provided as part of excitation system. For most applications an additional high set over voltage relay is sufficient. Time delayed under and over voltage protection may be provided.

71

71

Under & Over Voltage Conditions (2) Over Voltage Results from generator over speed caused by sudden loss of load. May be due to failure of the voltage regulator. An over voltage condition :

Š Causes overfluxing at nominal frequency Š Endangers integrity of insulation Under Voltage No danger to generator. May cause stalling of motors. Prolonged under voltage indicates abnormal conditions.

72

72

Other Protection Considerations

73

73

Pole Slipping Protection Simplified diagram of a generator

Stator

Rotor

X E G

E S

ZG9356 74

74

Pole Slipping Detection

E E = 2.8 (max) G S E E = 1.2 G S E E =1 G S

X R

E E = 0.8 G S E E = 0.19 (min) G S

MIS9357 75

75

Pole Slipping Protection Also referred to as Out of Step protection Techniques depends

Š on machine/system requirements Š Utility practices May be required to detect the first pole slip Could be time delayed to detect pole slips resulting in instability

76

76

Overfluxing Often applied to :-

Š Š

Generator transformers Grid transformers

Flux Ø ∝ V / f Caused by either :-

Š Š Š

Increase in voltage Reduction in frequency Combination of both

Usually only a problem :-

Š Š

77

during run-up or shut down can be caused by loss of load / load shedding

77

Transformer Magnetising Characteristic Twice Normal Flux

Normal Flux

Normal No Load Current 78

No Load Current at Twice Normal Flux 78

Magnetising Current with Transformer Overfluxed

ZG0780C 79

79

Overfluxing Effects of overfluxing :-

Š Š Š Š

Increase in magnetising current Increase in winding temperature Increase in noise and vibration Overheating of laminations and metal parts (caused by stray flux)

Protective relay responds to V/f ratio Co-ordinate with plant withstand characteristics Typical generator application Stage 1 - lower A.V.R. Stage 2 - Trip field

80

80

Over-Fluxing Relay

Ex

G

VT

AVR

81

RL

81

Low Forward Power Interlocking

Urgent Trip

Š Trip Directly to Circuit Breaker and Initiate shut down Š Risk of overspeed Š Examples :-

82

z

Generator Differential

z

stator ground fault

z

negative phase sequence.

82

Low Forward Power Interlocking Non-Urgent Trip

Š Trip governor Š Use low forward power interlocking to determine when main Circuit Breaker is tripped

Š Reduced risk of overspeed, and consequential damage to the machine Š Examples :-

83

z

Over voltage

z

Over load

z

Loss of synchronism

z

Field failure

83

Unintentional Energisation at Standstill Scheme

Typical Approach 50 &

27 & VTS

Trip

tPU tDO

z Overcurrent element detects breaker flashover or starting current (as motor) z Three phase undervoltage detection MiCOM-P340-84 84

z VTS function checks no VT anomalies 84

VT Fuse Failure Protection

Typical Voltage Balance scheme (60) Used for blocking purposes and for alarms Line voltage comparison done independently Fast Operating time May provide three outputs – Comparison VT fuse failure – Protection VT fuse failure – Protection block ZG7965D 85

85

Synchronising Relays Often applied to :-

Š Š

Synchronising of Generators Transmission line auto-reclose schemes

Synchronising of Generators

Š Š Š

Check voltage magnitudes Check slip frequency Check phase angle difference

Synchroscope

Š Š Š

86

Speed of rotation depends on slip frequency If frequencies matched, phase angle displacement indicated Does not indicate voltage magnitude

86

Voltage Checking & Comparators Voltage comparators often used in Transmission line autoreclose schemes :-

-

Live Line / Dead Bus

-

Dead Line / Live Bus

-

Dead Line / Dead Bus

Voltage monitors :-

87

-

Undervoltage monitor (e.g. Transmission Line)

-

Differential voltage monitor (e.g. Generator)

87

Auto-Synchronising Relays

Applied to Synchronising of Generators to control the machine Controls :-

Š Š Š

88

Filed current to adjust voltage magnitude Governor to adjust slip frequency Governor to correct constant phase displacement

88

Typical Schemes

89

89

Tripping Modes

90

Class A

HV breaker , Field breaker, Turbine For faults in the generator zone

Class B

Turbine Trip HV Breaker & Field Breaker interlocked with low forward power relay

Class C

HV breaker

90

Protection Package for Diesel Generator Connected Directly and Operating in Parallel with a Supply Authority Infeed

87 G

64 R 32

64 R

91

51 V

32

Reverse Power MWTU01

64R

Rotor Earth Fault MRSU01

64S

Stator Earth Fault MCSU01

51V

Voltage Dependent Overcurrent MCVG31

87G

Generator Differential MFAC34

91

Overall Protection of Directly Connected Generator Installation

Stator Earth Fault

64S

Rotor Earth Fault

64R

Differential Protection

87

51V Voltage Controlled O/C 46

Negative Phase Sequence

32 Reverse Power 40

Field Failure

81 Under / Over Frequency 27/59 92

Under / Over Voltage 92

Overall Protection of Generator Installation (1) Generator Feeder Protn. Overcurrent Voltage Restraint

51 V

Restricted E/F

Buchholz Winding Temp.

Reverse Power

32

Field Failure

40

Generator Differential Rotor E/F

64R

Overall Gen/Trans Diffl Protn.

93

87

Prime Mover Protection Negative Phase Sequence

Stator E/F

46

64S

93

Overall Protection of Generator Installation (2) Generator Feeder Protection O/C

Circuit Breaker Fail

Busbar Protection

Restricted E/F

Buchholz Winding Temperature

O/C + E/F

Buchholz

O/C

V.T.s Transformer Overfluxing Permissive (Low Power) Interlock

Standby E/F Restricted E/F

Pole Slipping

Field Failure Generator Differential

Unit Transformer Differential Protn.

Overall Generator Transformer Differential Protn.

Rotor E/F

Low Steam Pressure, Loss of Vacuum Loss of Lubricating Oil Loss of Boiler Water Governor Failure Vibration, Rotor Distortion Negative Phase Sequence

Stator E/F Protection

94

94

Embedded Generation

95

95

Embedded Generation

USED TO PROVIDE:

Emergency Power Upon Loss Of Main Supply Operate In Parallel To Reduce Site Demand Excess Generation May Be Exported Or Sold

96

96

ENGINEERING RECOMMENDATION G59

Relates To The Connection Of Privately Owned Generators & Generating Systems To Regional Electricity Companies

COVERS:

97

z

Safety Aspects

z

Legal Requirements

z

Operation

z

Protection

97

Co-generation/Embedded Machines

AR?

PES system

Islanded load fed unearthed

MiCOM-P340-98 98

98

Islanded Operation Must Be Avoided To Ensure: Unearthed Operation Of Main Supply Network Automatic Reclosure Of CB Will Not Result In Connecting Unsynchronised Supplies Staff Cannot Attempt Unsynchronised Manual Closure Of An Open CB Faults On Electricity Supply Companies Network Being Undetected Due To Low Fault Supplying Capability Of Embedded Generator Voltage & Frequency Supplied To Customers Remains Within Statutory Limits

99

99

PROTECTION Under/Over Voltage & Under/Over Frequency Keep Voltage & Frequency Within Statutory Limits Directional Power / Overcurrent Used When Generator Does Not Export Power During Normal Operation

100

100

PROTECTION Loss Of Mains Used Where Generating Capacity Is Closely Matched To Load Or Where Normal Operation Requires The Export Of Power Two Types Are Used:

ŠRate Of Change Of Frequency -

Sensitive Possible Nuisence Tripping

ŠVoltage Vector Shift 101

Requires Higher Change In load More Stable

101

PROTECTION ADDITIONAL PROTECTION

102

-

NEUTRAL VOLTAGE DISPLACEMENT

-

OVERCURRENT

-

EARTHFAULT

102