under voltage trip

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Al Ameen

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compressors rating 230V, it can be run even at 208V, already cable installed, now we face a problem when we start the 3 chillers each with two compressors, load increases there is a voltage drop go to 206V, so automatically compressors are shutdown, only 4 compressors or sometimes only one chiller run at a time.. give me the solution, cable already installed coming from Main distribution board running a length of 265 foot, 7 sets of 3*240mm copper cable to the load side distribution panel.
 

Jraef

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There are only 2 options that I can think of given the restrictions you posed:
  1. Only allow 2 chillers to run at any one time
  2. Increase the capacity of the system that is feeding power to them
You cannot change the voltage drop problem without changing something. So you either change the load, the conductor size, or the capacity of the transformer (or generator) that is feeding the system. You have already eliminated the option of changing the conductor size, and that was not guaranteed to solve the issue anyway if the power system capacity is too limited anyway.
 

broadgage

Senior Member
Location
London, England
When you say that the compressors can also run at 208 volts, do you mean that 208 volts is the absolute lower limit, that is it wont run at 207 volts, or do you mean that they will run on a nominal 208 volt system, which could be as low as 190 volts.

If the compressors are 230 volt nominal, with an absolute lower limit of 208, then it would appear that the wrong compressors have been specified.
230 volt compressors on a 208 volt nominal system=unlikely to work reliably.
The fact that they work at 208 volts, but not at 206 volts, does perhaps suggest that they are 230 volt nominal, with an abolute lower limit of 208.
The options would appear to be new compressors suited for the available service, or a new service to suit the available compressors, or voltage increasing transformers.

If however the compressors are suited for a nominal 208 volt service, and you have a 208 volt service, then they should work fine.
The fact that they dont suggests either a low utility voltage when heavily loaded, or excessive voltage drop in the installation.
 
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Jraef

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Good point. But given the metric cable dimensions, I would hazard a guess that the OP is not in the US so it's unlikely he has 208V power. 230V 3 phase power is very common in other parts of the world, 230V motor rating, +-10% puts him at 207V lower limit. They probably have an Under Voltage Relay set at 208V, a common thing in 230V countries.
 

kingpb

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Location
SE USA as far as you can go
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Engineer, Registered
Actually fellas, I would think that the system voltage is 400Y/230V, i.e. three phase or 115/230V single phase.

Based on the info provided, it would seem they may be 230V (line-line). The typical out of the box rating is going to be +/- 10% so the 207V works and the 206V does not.

Any who.........Suggested fix: Go find the transformer ahead of the equipment. Based on the voltage there is one somewhere up stream, and use the taps to get your 230V up to as much as possible. Probably the -5% is the max. that will be available to help, but that may be enough to keep you above the 208V needed.

If that doesn't work, your looking at a a soft starter, or VFD.
 

beanland

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Location
Vancouver, WA
Buck-Boost

Buck-Boost

If changing the source voltage at the service does not work, the other option is to install boost transformers to compensate for the voltage drop. If that is considered, it might be cheaper to replace the incoming copper conductors with something larger. Look at conduit size and determine largest copper wire that an be pulled. Does this solve the voltage drop problem? If conduit has to be replaced, not just conductor, boost transformer might solve.

Adding additional parallel runs of 3*240mm might also be cost-effective.
 

Al Ameen

Member
at jraef, u r right compressor nominal voltage is 230v adjustable range limit + or - 10%, relay is set to trip.. transformer range primary side 13800V secondary side 230/132V... i given two option to my operation manager, we can add three more cables or we can change do tap change in the transformer. if we set tap setting in the primary side to 13455V and giving 13800V i can have increase in voltage in secondary side may be more 6 to 7V. whether transformer will be damaged by doing this..
 

wirenut1980

Senior Member
Location
Plainfield, IN
I would advise against changing transformer taps to increase the voltage. The problem is a short duration voltage sag due to starting current. By raising the steady state voltage to account for the brief voltage sag, you risk having steady state voltage that is too high, and other equipment might get damaged.
 

skeshesh

Senior Member
Location
Los Angeles, Ca
I would advise against changing transformer taps to increase the voltage. The problem is a short duration voltage sag due to starting current. By raising the steady state voltage to account for the brief voltage sag, you risk having steady state voltage that is too high, and other equipment might get damaged.

That's an interesting comment. Sure there is the possibility of such a problem but is it really enough a worry to advise against changing the taps? We're talking about raising the steady state voltage very slightly here, so I'd be interested to know what voltage you would consider too high for this system and also what type of load you'd be most concerned about.
 

kingpb

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Location
SE USA as far as you can go
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Engineer, Registered
Certainly you have to be conscious of over voltage when the bus is lightly loaded. During steady state operation it should not be an issue, but still worth taking a look at a voltage meter.

LV switchgear can withstand a constant over-voltage of at least 10%. Would have to check manufacturers data to know the exact capabilities, but unless the system voltage on the HV side of the transformer is more than 5% over nominal, then the increase of 5% on the LV side using taps should not be a problem. Possibly you might be able to get away with using the 2.5% taps.

This is a viable solution to bus voltage issues although for some reason rarely looked at.
 
I would advise against changing transformer taps to increase the voltage. The problem is a short duration voltage sag due to starting current. By raising the steady state voltage to account for the brief voltage sag, you risk having steady state voltage that is too high, and other equipment might get damaged.

Could,but can't say with certainty that it will without running a load study. The tap increase and lowering the UV trips are both options that should be considered, again, with proper calculations.
 
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