How to control Power Factor

 What is Power Factor? 

Power Factor is an expression of energy efficiency. It is usually expressed as a percentage; and the lower the percentage the less efficient power usage is. 

Power Factor expresses the ratio of true power used in a circuit to the apparent power delivered to the circuit. A 96% power factor demonstrates more efficiency than a 75% power factor. Power Factor below 95% is considered inefficient. 

Power Factor is the measure if how effectively your business uses its electricity. It is the ratio of real power (MW) to apparent power (MVAR). A site with low power factor draws more apparent power than real power (importing). So, if your power factor is low, you may be paying more than you need to for your electricity. 

How to Control Power Factor

1.)   Before synchronizing the Generator to the Grid, check OLTC setting; OLTC default setting is 13  

2.)   Upon synchronizing the Generator to the Grid, adjust the OLTC as per Voltage of the Grid. A corresponding HV is set vs LV. 

3.)   If the Step-up Transformer Voltage is higher than the Grid, reactive power will be exporting and if Step-up Transformer Voltage is lower than the Grid, reactive power will be importing. 

4.)   Ideally power factor is to be set at unity 1 but it is difficult to achieve. This is due to varying reactive power from various motors connected to the grid. 

5.)   Importing and Exporting of Power Factor affects 52G Circuit Breaker; Monitor the Amperes of the Circuit Breaker upstream to the Grid. Take note of the tripping setpoint of the Circuit Breaker on Current. 

6.)   If importing reactive power, increase Generator Voltage 

7.)   If exporting reactive power, decrease Generator Voltage 

8.)   Monitor closely Grid frequency during Generator Voltage variation 

9.)   If the Generator Voltage is maxed out whilst increasing/decreasing, it is time to change the tap:

a.     Lower Tap Position > Higher Generator Voltage

b.     Higher Tap Position < Lower Generator Voltage

10.) If the Tap Position of the Step-up Transformer is maxed out, and the Generator Voltage is still far off to the Grid, asked Western Power to energize their Capacitor Bank 

11.)  Otherwise, Operator can adjust the Grid Voltage by asking other Power Plant (Bigger Plant) to minimise their Step-up Transformer to a sustainable Grid Voltage. 

Logic example: 

Say the grid voltage is at 135.6 kV, we should aim to produce the same Voltage or higher by selecting the appropriate Tap Position corresponding to the Grid Voltage. If Generation is not greater or lower than the grid voltage, we will be importing reactive power and subsequently dropping our power factor in the process and minimising our generation due to high import of reactive power. Furthermore, high import of reactive power will cause overheating of Generator Stator end winding and high operation cost. Generator Efficiency will be diminished. 

 

1, 2 SUT 

Tap Position	HV	HV amps @ 67.5 MVA	HV Amps @ 90 MVA	LV
1	151800	257	342	11000
2	150150	260	346
3	148500	263	350
4	146850	266	254
5	145200	269	358
6	143550	272	362
7	141900	275	366
8	140250	279	371
9	138600	282	375
10	136950	285	379
11	135300	289	384
12	133650	292	389
13	132000	296	394[ds1]
14	130350	300	399
15	128700	304	404
16	127050	308	409
17	125400	311	414

 

3, 4 SUT 

Tap Position	HV	HV amps @ 67.5 MVA	HV Amps @ 90 MVA	LV
1	151800	257	342	11000
2	150150	260	346
3	148500	263	350
4	146850	266	254
5	145200	269	358
6	143550	272	362
7	141900	275	366
8	140250	279	371
9	138600	282	375
10	136950	285	379
11	135300	289	384
12	133650	292	389
13	132000	296	394[ds2]
14	130350	300	399
15	128700	304	404
16	127050	308	409
17	125400	311	414

 

4, 5 SUT 

Tap Position	HV	HV amps @ 67.5 MVA	HV Amps @ 90 MVA	LV
1	151800	257	342	11000
2	150150	260	346
3	148500	263	350
4	146850	266	254
5	145200	269	358
6	143550	272	362
7	141900	275	366
8	140250	279	371
9	138600	282	375
10	136950	285	379
11	135300	289	384
12	133650	292	389
13	132000	296	394[ds3]
14	130350	300	399
15	128700	304	404
16	127050	308	409
17	125400	311	414

 

7 SUT 

Tap Position	HV	@ 67.5 MVA	@ 90 MVA	LV
1	151800	257	342	11000
2	150150	260	346
3	148500	263	350
4	146850	266	354
5	145200	269	358
6	143550	272	362
7	141900	275	366
8	140250	279	371
9	138600	282	375
10	136950	285	379
11	135300	289	384
12	133650	292	389
13	132000	300	399[ds4]
14	130350	304	404
15	128700	308	409
16	127050	308	409
17	125400	311	414

 

9 SUT 

Tap Position	HV	ONAN	ONAF	LV
1	151800	380	532	11000
2	150150	385	536
3	148500	389	544
4	146850	393	550
5	145200	398	557
6	143550	402	563
7	141900	407	570
8	140250	412	576
9	138600	417	583
10	136950	422	590
11	135300	427	597
12	133650	432	605
13	132000	437	612[ds5]
14	130350	443	620
15	128700	449	628
16	127050	454	636
17	125400	460	645

 

11 SUT 

Tap Position	HV	ONAN	ONAF 1	ONAF 2	LV
1	151800	323	399	532	15000
2	150150	327	404	538
3	148500	330	408	544
4	146850	334	413	550
5	145200	338	418	557
6	143550	342	422	563
7	141900	346	427	570
8	140250	350	432	576
9	138600	354	437	583
10	136950	358	443	590
11	135300	383	448	597
12	133650	367	454	605
13	132000	372	459	612[ds6]
14	130350	376	465	620
15	128700	381	471	628
16	127050	386	477	636
17	125400	391	483	545

 

9 Step down Auxiliary Tx – 11kV to 3.3 kV 

Tap Position	HV	LV
1	11825	3450
2	11550
3	11275
4	11000[ds7]
5	10725
6	10450
7	10175

 

9 Step Down Auxiliary Tx – 3.3kV to 415V 

Tap Position	HV	LV
1	3548	433
2	3465
3	3382
4	3300[ds8]
5	3218
6	3135
7	3052

 

9 Unit Transformer 

Tap Position	HV	LV
1	23100	415
2	22550	415
3	22000	415[ds9]
4	21450	415
5	20900	415

 

11 Unit Transformer 

Tap Position	HV	LV
1	15750	6900
2	15375	6900
3	15000	6900[ds10]
4	14625	6900
5	14250	6900

 

·       Over Excitation Limit (OEL) = limits the generator operating in the overexcited region to within the generator capabilities curve.

·       Under Excitation Limit (UEL) = prevents the AVR from reducing excitation to such a low level that the generator is in danger of losing synchronism, exceeding machine under-excited capability or tripping due to exceeding the loss of excitation protection setting.

o   Typical setting of OEL and UEL is 5% of Generator Voltage rating 

 

MVAR

LEADING

LAGGING

·      Operate within the region of Stator Winding 

·      MVAR > 0 = Lagging 

·      MVAR < 0 = Leading 

·      MVAR = 0 = Unity 

LEADING = Capacitive Load 

LAGGING = Inductive Load 

 

 

 

Generator Protective Device 

Function Numbers	Description
15	Synchroniser
21	Distance Protection / Back-up for System general zone phase faults
24	V / Hz Protection
25	Synch Check Protection
27	Under Voltage
32	-        Reverse Power Protection  -        Anti-motoring for Generator
40	Loss of field Protection
46	Stator unbalanced Circuit Protection
49	Stator Thermal Protection
50B	Instantaneous over current Protection
51 GN	Time over current protection / Back-up for Generator Ground Faults
51 TN	Time over current protection / Back-up for ground fault
51 V	Voltage controlled time over current protection
59	Over voltage protection
59 BG	Zero sequencing Voltage protection
59 GN	-        Voltage Protection  -        Ground fault protection for Generator
60	Voltage Balance Protection (Protection for Blown Fuse)
61	Time over current protection
62 B	Breaker Failure Protection
64 F	Primary protection for rotor ground fault
78	Loss of synchronization protection
81	Over and under frequency protection
86	Hand reset lock-out auxiliary relay
87 B	Primary phase-out fault protection for generator
87 GN	Sensitive ground fault protection for generator
87 T	Differential protection for Transformer
87 U	Differential protection for overall unit protection of generator and transformer
94	Self-reset auxiliary tripping relay

 

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 [ds1]Default Tap Position 

 [ds2]Default Tap Position 

 [ds3]Default Tap Position 

 [ds4]Default Tap Position 

 [ds5]Default Tap Position 

 [ds6]Default Tap Position 

 [ds7]Default Tap Position 

 [ds8]Default Tap Position 

 [ds9]Default Tap Position 

 [ds10]Default Tap Position