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I have the problem described below and think that fitting an isolating transformer might solve it. If, you agree we want to know prices of equipment
We have a problem at a remote site in Africa where we are running a couple of prime power generator sets (FG Wilson 220/380, 50 Hz (1500 rpm) 450 kVA (409 kVA prime power) single set operation, no synchronization, controlled by a transfer switch. The alternator is connected star, and earth neutral TNS connection is provided inside the unit. The system is running during normal operation at between 40 and 50% of the prime power rating, which should not present us with problems, ambient temperatures remaining constant at around 30 – 32 degrees Celsius. We are at sea level. The connected load is around 65% inductive, comprising reefers, chiller/freezer units –the remaining 35% is made up of general single phase small power and lighting for offices and accommodation. The phases are balanced to within around 5%.
Our problem is that we also supply power to our landlord, who has a construction yard. He uses a lot of heavy duty three phase equipment such as pressing machines and industrial wood saws. There is obviously a fluctuating load on his site, something between 40 and 45 kVA.
When this equipment is being used on the site, the inrush current is causing voltage dips, predominantly on L3, which drops top around 160 volts. We have all gthe usual symptoms – lights flicker and compressors are in constant need of repair. Due to complicated inter-company politics, it is not possible to implement the obvious solution of supplying the landlord’s installation from a separate generator.
I was thinking that an isolating transformer might be a solution – but I am in need of further technical advice.
 

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What type of governor are you utilizing on the generators? Seems the loads are not that significant to result in this if you are utilizing properly adjusted electronic governors.

Fuel supply and filters acceptable?

Another option could be a soft start on his motors.

Have you had the generator fully tested and checked for any voltage, regulator issues as well as the governor.
 

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brian john said:
What type of governor are you utilizing on the generators? Seems the loads are not that significant to result in this if you are utilizing properly adjusted electronic governors.

Fuel supply and filters acceptable?

Another option could be a soft start on his motors.

Have you had the generator fully tested and checked for any voltage, regulator issues as well as the governor.
I agree on all points. I'll just add that an isolation transformer will do nothing for you except possibly make it worse, because the transformer will have an onrush current too.
 

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I agree on all points. I'll just add that an isolation transformer will do nothing for you except possibly make it worse, because the transformer will have an inrush current too.

I should have added that, it sure won't minimize any issues.
 

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Bilge Rat
motors and controls.........
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I think what the OP is getting at is a transformer between his system and the landlords system.

If so, a transformer with high enough impedance will cause less voltage dip at the generator, but more at the landlords system.

A current-limiting reactor might be a better choice though.

One drawback is that the landlords voltage will dip WAY low when a large motor starts.

As noted, some sort of soft-start at the big motors would be the best solution. If the motors cannot be started wye/delta or part-winding, an autotransformer or electronic soft-start would work.

One possibility is an inline soft-start. This unit is installed between the existing starter and the motor. When the starter is energized, it gradually increases current to the motor. They cost a bit less than a stand-alone soft-start.

The only ones I'm familiar with are Allen Bradley bulletin 154.

Rob
 
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