250 Hp motor running 225 amp + 152 Kw @ 60Hz. 50 Hz Operation?

[racookpe1978]

50 Hz/60 Hz operations have been discussed before - The FAQ sheets in this forum were useful. Thank you. I also reviewed all threads going back to January this year, but saw nothing exactly like this problem.

Nameplate Data:
Frame 449TS, rated 460 volts @ 272 amp.
NEMA 3, 3 phase TE 8404 (B404 ?)
250 Hp 60 Hz/1780 rpm
Westinghouse brand

Background. This question was asked in the pump forum - and several good points brought, solved, and resolved. Several readers there recommended that the motor issues be addressed here:

I have a large portable US-built oil filter system that (now) can only run properly in Europe's 50 by renting an temporary 60 Hz generator and fuel tank.

Obviously, renting the generator is too expensive nowadays (several tens of thousands of Euro's), hurts sales and increases costs and setup time (crane time, truck rental, space, etc.)

Boss wants to use the current motor at 50 Hz instead.

Temporary Generator output now, while the pump is running in a "standard flush configuration:

464/458/456 volts on the three phases
214/225/220 amps
.89 pf using 149 - 152 Kw.

If I run at 1450 rpm (nominal 1500 for 50 Hz) instead of 1800 rpm from the generator's 60 Hz, my flow is too small. (Pump is a ITT 10x12x14 3405 type with a max impeller, flow spec is 4200 gpm minimum.)

if I change pumps (and use the same motor at but at the European 380-420 volts and 50Hz ) to the larger 10x12x17 casing, It appears I can regain the flow and keep in the same 3405/3410 "family" so my baseplate still fits.

Filter, suction and discharge piping would stay the same, so I expect the resistance to be the same.

The new casing moves the pump suction and discharge lower by 1 inch - but physically I can shim up motor and pump casing back to old height. Left right distance can be compensated for.

1) Running time for the flushes is 120 to 160 hours, but the pump will only be used for a few weeks every year.

2) A a lower speed and lower voltage, the motor heats up more. Can I calculate this extra heat or even estimate it?

3) At a lower speed there is more current: Is the nameplate rating of 272 threatened? Actual auxiliary voltage on the power plant's system panels varies a little, but is displayed as 400 VAC, 388 VAC, and 390 VAC.

4) Any other problems anybody can foresee? Softstart motor controller manual says it is rated for 50 Hz ops after a switch is changed on the control box.

 

[JohnWaa]

A a lower speed and lower voltage, the motor heats up more. Can I calculate this extra heat or even estimate it?

You probably can get an external cooling fan kit for your motor. If not, mount a large muffin fan to the rear of the motor (I've done this in the past and it works very well).

As for the loading of the motor, check with an applications engineer at the pump company. They should be able to tell you what kind of load the pump will put on the motor.

 

[waross]

I have seen motors rated for either 50 or 60 Hz but they have always been the 50/60 Hp ratio. I have never seen derating for increased heat at the lower frequency.
Your first and most important consideration should be:
Will the motor have enough HP at 50 Hz to give the flow needed at the head needed.
Your 250 HP motor will derate to 208.33 HP at 50 Hz. If your pump guy tells you that you will need more than 208 HP, then forget it. Buy a VFD and voltage matching autotransformer.
If you need exactly 208.33 Hp AND the ambient is at the maximum allowable, then heating may be an issue. For the majority of applications, there is enough spare thermal capacity in the motor either from less than 100% loading or from less than maximum ambient temperatures that slightly reduced cooling of the motor is not an issue.
Voltage may be an issue. If you cannot maintain the Volts per Hertz ratio with available voltage, buy a matching transformer. Your two main worries are;
1> Need more than 208 Hp at 50 Hz.
2> Your 50 Hz voltage is not 50/60 of 460 Volts. (383 Volts)
If you satisfy these two issues, you are good to go.
Even if you are at the maximum on all parameters, the reduced life of the motor from slightly elevated temperature may not be an issue with the low duty cycle on the motor.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[LionelHutz]

According to BigInch over on the pump forum, changing to get the same head at 50Hz will overload the motor. I would have though the same head and flow would still have the same power but he claims more so I'd tend to believe that.

Personally, I'd just get a VFD.

At 390VAC supply, the motor is capable of;

390V/460V * 250hp = 212hp = 158kW

Since the load is 152kW, you could actually run the motor at the reduced voltage and 60Hz and it should still work fine. This is similar to using a 212hp, 50Hz rated motor and running it over-frequency in the constant HP range.

I expect this is a fairly new motor and if so, it will be fine working on a VFD. The motor manufacturers use the same enamel wire in all their motors and use the same manufacturing facility for all their motors, so if they build a specific "VFD rated" motor it's more than likely just a nameplate change.

So, the first solution is just a VFD to run at the higher frequency.

If you are not convinced that will work, then use a step-up transformer or boost transformer configuraton. I bet Bill could give a good suggestion on some smaller tranformers to use in a boost configuration instead of full step-up transformer.