Transformer Power Factor

We don't like all caps.

What is the load on the transformer on non-working hours? It is likely to be very low (may be only a few percentage of lighting load.)

Under this condition the poor power factor is expected.

Transformer reactive (magnetising KVAr) is constant, where as the active KVA is almost nil.

APFC usually, and for you correctly, put on load side hence does not compensate for the transformer KVAr.

In fact the low pf on the low load condition really does not matter since your power demand is low too. So this really does not affect the average pf of the plant.

However if you are really uncomfortable (and wish to spend a few $), put a fixed capacitor bank on the HT side or simply switch off the transformer on off hours, and put an auxiliary transformer , or battery bank/ inverters etc, solar panels,... for the off-hours lighting/load.

25 kvar fixed capacitor at low voltage side and instalet before the main cb (of corse you must fused with the corect fuses ) will corect your problem .

you work only 8 hours and 16 you are off load .readings of cos f from your supplier are get 3-4 times per hour .and drop down your average pf.

Even assuming the no load for 60 Hrs

Assuming pf of transformer at FL is 0.99

The KVAr will be approx 60 (rounding off to next 10)

Total KVAr in 24 Hrs = 1440 KVAH

At full load say you have 300 KW connected load)

KVA_active = 300*8 = 2400 KVA in 8 hrs

power factor (averaged over the day) even in this condition will be

cos(tan^-1(1440/2400) = 0.857

which is not very good but not very bad either. I don't think it is in penalty region.

Putting a fixed cap bank in HT line will of course help, but you may have to take necessary permissions from the autorities. Better to disconnect the transformer in offload period.

mail on ezp@ctr.in.

i believe that switching on-off the breaker of HT is not the right way .

mechanikal life of this type of breaker is limited to 1-2000 actions and they cost

a few .000 k . if you act 2 times at day and 290 days per year you are close to life limit. also capasitors at HT 11kv side is also expencive and you must consider

what happens if start to act in reverse way due to voltage problems and the capacity of the line which is long in some cases.any way you need a breaker and fuses for the HV capacitor also alot of money.