No amps on one phase

THENORTHSIDER

3 phase motor Star connected. Phase 1 is taking 0.7 of an Amp, phase 2 the same and the 3rd phase is drawing no current.

Motor is running

WHY :eek:

frankmul

Does it sound ok, it can still run single phasing if it's under no load

THENORTHSIDER

it's driving a bridge on a clarifier, with a gear box that the ratio makes the bridge move slowly.

I have 380 volts between phases and 230v between each phase and a neutral point.

Why is it single phasing?

Only noise from it is a clicking sound but we think that's a gearbox issue.

Bruthal

Where did you take the voltage readings?

Luckysasha

Could be a problem with the winding. It would still show voltage at the terminal box. You could try meggering the windings themselves with the 3phase wires removed.

Bruthal

Luckysasha wrote: »

Could be a problem with the winding. It would still show voltage at the terminal box. You could try meggering the windings themselves with the 3phase wires removed.

Ordinary multi meter better for checking for open circuits than a merger is.

THENORTHSIDER

thanks lads for the help, I'm in tomorrow so will check all your suggestions. Because its on a rotating bridge there is a brush system to connect the cable to the bridge that will be my first port of call.

THENORTHSIDER

Top of my head burnt to a crisp but problem solved

Checked all connections from MCC to motor. Found that the last person to connect the motor clamped onto the insulation on the terminal and not onto the terminal itself. remade the terminal and happy days all working.

The current demand is now a balanced 0.4 A, 0.4A and 0.6 A.

Even with only two phases the current demand on them did not go higher than the FLC.

Thanks again for all suggestions.

Luckysasha

Just remember to check the overload on the contactor. It should be 1.25 x the starting current and not the running current. I've seen that mistake made many times during commissioning.

Bruthal

Luckysasha wrote: »

Just remember to check the overload on the contactor. It should be 1.25 x the starting current and not the running current. I've seen that mistake made many times during commissioning.

If it was set at 1.25 times starting current, the overload would seem pointless. No?

Starting current can't really be exceeded, unless the motor is rotating in reverse at the instant of starting.

2011

I would have expected the overloads to be set at the full load current of the motor.
Starting current is generally 3 to 5 times full load current (for DOL).

Tuco88

I always went by the info on the nameplate of the motors FLC and figured the nice guys at ABB had take all this into account at some point, and I always set the overload just a little less to be safe. Resetting/replacing an overload no worries, the risk of a burnt out motor?