Required Load Bank

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Orlyboy

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Hi to everyone,

We have an ongoing FEED project for replacement of old substation. The substation is to be demolished and replaced with new one.
The substation requires to have a dedicated emergency diesel generator. We have sized the generator based on the connected loads.
The generator details is as follows:

630 kVA, 440V, 50Hz.

Questions:
1. What would be the required Load Bank for the given size of emergency standby generator?
2. What would be the conductor size?
3. What would be the OCPD required?

Please show me calculation for the given and required conditions.

Your idea is highly appreciated.

Thanks and regards
 
My guess would be that whatever entity is requiring the load bank would be a better source of information on how to size it than a group of more or less random folks on the internet.

As for rating of the OCPD for the load bank, most times either the generator OCPD protects the load bank or it has its own protection. This question is best answered by the manufacturer of the load bank.

As for conductor sizing, that is dependant on the required ampacity based on whatever load you are planning to put on the generator via the load bank. Until you know the load bank size, you can't determine this.
 
Last edited:
Orlyboy said:
Hi to everyone,

We have an ongoing FEED project for replacement of old substation. The substation is to be demolished and replaced with new one.
The substation requires to have a dedicated emergency diesel generator. We have sized the generator based on the connected loads.
The generator details is as follows:

630 kVA, 440V, 50Hz.

Questions:
1. What would be the required Load Bank for the given size of emergency standby generator?
2. What would be the conductor size?
3. What would be the OCPD required?

Please show me calculation for the given and required conditions.

Your idea is highly appreciated.

Thanks and regards
Click to expand...

1. Is the load bank for periodic testing of the generator when it is in standby? If so, the load would need to be about 500kW for full load. Generators are often rated at 0.8pf.
2. The rated current is about 830A. Conductor size depends on ambient, type of cable, method of installation, overcurrent protection, regulations applicable in the region where the equipment is to be installed.....
 
Besoeker said:
1. Is the load bank for periodic testing of the generator when it is in standby? If so, the load would need to be about 500kW for full load. Generators are often rated at 0.8pf.
2. The rated current is about 830A. Conductor size depends on ambient, type of cable, method of installation, overcurrent protection, regulations applicable in the region where the equipment is to be installed.....
Click to expand...

1. Yes, the load bank is designed for periodic testing.
2. From this info, therefore I presume that whatever the size of the genset just take the True power and that will be equivalent to the load bank as it is said "Resistive Load".

Appeciate all the replies.

Thanks
 
For calculation of OCPD, you need to take not the size of the generator i.e 630KVA but the size of the load bank i.e 500kW. Divide it by 1.732x440 and get a value of 656A. If your periodic testing is more than 3 hours, multiply 656 by 1.25. The result 820A. Round it down to 800A. Your OCPD size is 800A.
 
Sahib said:
For calculation of OCPD, you need to take not the size of the generator i.e 630KVA but the size of the load bank i.e 500kW. Divide it by 1.732x440 and get a value of 656A. If your periodic testing is more than 3 hours, multiply 656 by 1.25.
Click to expand...
Why the 1.25?
 
The load bank would need to be big enough to run the DEG without it causing wet stacking of the DEG. Talk to manufacturer, they will tell you what is needed.
 
Sahib said:
3 or more hours loads require 1.25 and for loads of lesser duration, drop it. Per NEC.
Click to expand...
What makes you assume that NEC applies in this instance?
See the point I made above:

2. The rated current is about 830A. Conductor size depends on ambient, type of cable, method of installation, overcurrent protection, regulations applicable in the region where the equipment is to be installed.....
 
Orlyboy said:
... The substation requires to have a dedicated emergency diesel generator.

Questions:
1. What would be the required Load Bank for the given size of emergency standby generator?
Click to expand...

Orly -
You already have pretty good answers, I have nothing to add there. However I do have a curiusity question:

Why bother with a loadbank? Just sync to the bus, parallel to Normal supply, load up the generator pushing the power to the load.

Generally, most systems of this type have the paralleling gear, if for no other reason than to provide a seamless tranfer when returning to Normal supply.

No extra cost for load bank or load bank maintenance.

Just curious

ice
 
ice:The diesel generator need to be tested for its operational readiness periodically. Its prime mover diesel engine also need to be tested at full load and over load. This can be easily done with heater banks. But in grid paralleling,operation of generator at a specific power factor may not be always ensured.
 
Sahib said:
ice:The diesel generator need to be tested for its operational readiness periodically. Its prime mover diesel engine also need to be tested at full load and over load. This can be easily done with heater banks. But in grid paralleling,operation of generator at a specific power factor may not be always ensured.
Click to expand...

Huh?? Of course it can. That's what the voltage knob is for. It will change the field DC drive - And that will change the gen pf. The grid will either import or export vars to match.

As for a load bank that provides an .80pf load - they are available but extremely rare and damned expensive.

However, I expect the answer to be: Because we wish to do an end to end test, verifying the dead bus start and come on-line, to work as well as testing the gen will accept rated load. And I would be surprised if the required loadbank will be anything other than resistive.

ice
 
iceworm said:
Huh?? Of course it can. That's what the voltage knob is for. It will change the field DC drive - And that will change the gen pf. The grid will either import or export vars to match.As for a load bank that provides an .80pf load - they are available but extremely rare and damned expensive.ice
Click to expand...
1)Keeping pf steady might require automatic control;more complication.2)Generally,only the prime mover in a genny is tested for load taking for which resistors suffice.
 
Sahib said:
1)Keeping pf steady might require automatic control;more complication.
Click to expand...
It isn't our main line of business but we do design and manufacture AVRs from time to time. Every one I've done in the past forty some years has had the facility, not always used, to control power factor.

Sahib said:
2)Generally,only the prime mover in a genny is tested for load taking for which resistors suffice.
Click to expand...
Only?
The prime mover produces a mechanical output. As far as I know, resistors are not designed to take a mechanical input.
 
The generator portion is used in the process, but is not being tested to its limit the way the prime mover is.
To fully exercise the generator requires a reactive component to the load.
 
GoldDigger said:
The generator portion is used in the process, but is not being tested to its limit the way the prime mover is.
To fully exercise the generator requires a reactive component to the load.
Click to expand...
You may be correct but the logic escapes me.
Generally, electrical machines are ultimately limited thermally*. Loading the generator to it's maximum rated current at any power factor will surely test that thermal limit won't it?

*As an aside, the thermal limit applies to most electrical items.
Try pushing 100A down a bit of 1.0mm2 (equivalent to 17AWG) and its life expectancy will be in the order of a few seconds.
Fun to watch but - don't try it at home........:D
 
Besoeker said:
What makes you assume that NEC applies in this instance?
See the point I made above:

2. The rated current is about 830A. Conductor size depends on ambient, type of cable, method of installation, overcurrent protection, regulations applicable in the region where the equipment is to be installed.....
Click to expand...
Trust me.
 
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