Phase Protector

[faresos]

Hello Everyone,

Does anyone has experience with how to protect an existing main switchboard and MCC (800A, 480Y/277V) from a loss of a phase? I was told the base where the building is located has several issues in the past with losing a phase at the transformer which is causing some issues for the some equipment such as starters and VFD's? I believe the starters are equipped with ingle phasing protection but not sure about the VFD's since they came as part of the HVAC package.

Any thoughts ?

 

[Jraef]

Most VFDs will have either a Phase Loss Trip protection scheme, or don’t actually care about phase loss until the DC bus ripple gets too bad (AB drives are like this). So if the load is light, as it would be on an HVAC system running at less than 75% capacity, the VFDs might not even know there was a phase loss on the input and keep chugging along. YMMV, you need to read the manuals on the drives.

The most common approach however is to have one phase monitor relay at the incoming service, then take its contact into your overall control system to have it shut down anything that would be affected.

 

[petersonra]

Most VFDs will have either a Phase Loss Trip protection scheme, or don’t actually care about phase loss until the DC bus ripple gets too bad (AB drives are like this). So if the load is light, as it would be on an HVAC system running at less than 75% capacity, the VFDs might not even know there was a phase loss on the input and keep chugging along. YMMV, you need to read the manuals on the drives.

The most common approach however is to have one phase monitor relay at the incoming service, then take its contact into your overall control system to have it shut down anything that would be affected.

VFDs these days are generally pretty good at protecting themselves.

 

[faresos]

Thanks all for the reply.

so does the loss-of-phase protector protects the starters/VFD's or motors only? There are several starters and VFD's got damaged and no mentioned of damaged motors.

Thanks,

 

[petersonra]

Thanks all for the reply.

so does the loss-of-phase protector protects the starters/VFD's or motors only? There are several starters and VFD's got damaged and no mentioned of damaged motors.

Thanks,

I am surprised any VFDs were damaged. They usually protect themselves pretty well.

The motor starter probably won't care but the motors they control will not like being single phased for any length of time. best to just trip the starters and shut the motors off if a single phase condition is detected. Most likely the starters will not run real long anyway before they trip on overload if a phase is gone. if the motor starter has single phase protection it should have tripped almost immediately, long before the motor starter was damaged.

I wonder if you actually had a loss of phase or if it was something else.

 

[Jraef]

I am surprised any VFDs were damaged. They usually protect themselves pretty well.

The motor starter probably won't care but the motors they control will not like being single phased for any length of time. best to just trip the starters and shut the motors off if a single phase condition is detected. Most likely the starters will not run real long anyway before they trip on overload if a phase is gone. if the motor starter has single phase protection it should have tripped almost immediately, long before the motor starter was damaged.

I wonder if you actually had a loss of phase or if it was something else.

I agree, probably something else that happened at the same time, or first. If a 3 phase motor is running WHEN the phase is lost, it will keep running under single phasing conditions and if the load is light on the motor, it may run like that for a long time, damaging the motor if the OL relay is not designed to detect it. But that wouldn't damage the starter.

 

[faresos]

would a surge occurs if you lose a phase that might damaged the VFD's? I will need to verify if the VFD is equipped with SPD but I know the main switchboard has SPD.

 

[petersonra]

would a surge occurs if you lose a phase that might damaged the VFD's? I will need to verify if the VFD is equipped with SPD but I know the main switchboard has SPD.

What kind of damage was done to the VFDs? Did by any chance the protective MOVs explode? i suppose if you had a delta power system and you lost a phase that might cause a L-G MOV to explode.

I don't know what could damage a starter though. Starters are pretty hard to hurt. usually in my experience the overloads will fail before the starter itself is damaged.

 

[Russs57]

Are they willing to have all power shut off to building? If so surge suppressor on line side of main breaker with LED’s for each phase (so they know when they have all 3 phases), then phase monitoring to activate shut trip coil on main breaker.

Most motor starters with solid state overload relay will trip on single phase conditions. About the worst I have seen on VFD’s is drive tries to run on one less pair of diodes and over current blows remaining diodes. Newer/better drives shouldn’t let this happen.

The real damage is if you have any 3 phase 480 to 208/120 transformers that are being single phased. Two out of the 3 legs on the secondary side will have low voltage. Typically 120 equipment has little protection and I have seen significant equipment damage in these situations.