Modeling Chiller Motors for Fault Contribution

[philly]

When modeling large Chiller motors for a fault study should these chiller motors be modeled as motor loads capable of fault current contribution during a fault, or should these be modeled as loads which are not capable of fault current contribution?

I was told once that compressor motors do not contribute any fault current due to the fact that there is no rotating mass. I'm not sure if Chiller motors fall under the same category.

If these motors motor are capable of fault contribution what is the best way to determine equivelent motor HP size. Most chillers I have seen have a kW rating, and/or a RLA, and LRA rating. Is there a rule of thumb for converting this nameplate information to an equivelent Hp size for modeling puposes?

If modeled as a motor what X" is typically used? Is the 17% figure used for single large motors used or would something different be used?

 

[transient]

hi

hi

HI please see my replies in RED .

When modeling large Chiller motors for a fault study should these chiller motors be modeled as motor loads capable of fault current contribution during a fault, or should these be modeled as loads which are not capable of fault current contribution?
Yes ,the feeder and the motor should be considered as the fault source . and if there's a fault current , it should trip the nearest breaker .
I was told once that compressor motors do not contribute any fault current due to the fact that there is no rotating mass. I'm not sure if Chiller motors fall under the same category.
i hope , we are talking about short circuit faults , grounding faults , overcurrents , if yea , then I am not sure then if rotation of mass is relevant in this context.

If these motors motor are capable of fault contribution what is the best way to determine equivelent motor HP size. Most chillers I have seen have a kW rating, and/or a RLA, and LRA rating. Is there a rule of thumb for converting this nameplate information to an equivelent Hp size for modeling puposes?
Suppose your motor is 10 KW , then mutliply it by 1.34 you will get the rating in HP.
If modeled as a motor what X" is typically used? Is the 17% figure used for single large motors used or would something different be used?Better check motor name plate characteristics ,one example for you ==> 500HP , 1800RPM , Xd"=16.7% , X/R=19.3

Transient ..

 

[wallypiper]

Just a heads up on chiller ratings.

Chiller KW ratings may be referring to electrical load but if it is a unit imported from Europe or Asia, it may be stating refrigeration capacity. Although most US equipment has it's refrigeration capacity listed in tons or btu/h, equipment originating outside the US may be rated in KW. 1 KW = 3412 btu/h or 1 ton = 3.5 KW. However, typical electrical load from a large chiller is around 0.5 to 0.6 KW/ton. So a 500 ton chiller (6,000,000 btuh) will typically have an electrical load of around 250 KW but a refrigeration capacity of 1758 KW. So, just because a value has KW written next to it, don't assume it is an electrical rating. The same is true of European or Asian motors which have a nameplate power rating in KW but you cannot convert that directly to amps using the familiar formulae for KW to amps. The KW rating on the nameplate is shaft power, not electrical load. As stated, you can convert that number to HP (KW x 1.34) and use that to determine amperage.

All US made chillers I have ever seen (hundreds from 10 tons to 600 tons) include MCA, RLA and LRA on their nameplate or in the published data available. That's minimum circuit ampacity, rated load amps and locked rotor amps. Refrigeration equipment gets special treatment in the NEC. MCA is based on rated load amps rather than the maximum theoretical horsepower rating of the motor or motor nameplate data (if it exists). Two chillers may have the same physical motor mounted on them but different RLA and MCA ratings. I think if you want to come up with an equivalent HP rating for the motor itself, you would use the LRA, not to size a feeder, which is based on RLA, but for a calculation based on actual motor characteristics.

I don't understand how a compressor, whether it's a refrigerant compressor or an air compressor, could be considered to have no rotating mass. How is the term used if that is correct?

 

[beanland]

VFD Impact

VFD Impact

If the chiller uses a solid state variable frequency drive, as is typical of newer chillers, there is no fault contribution. Only if the chiller is connected across the line as an induction or synchronous motor would there be fault contribution.