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Rail supply lines are intentionally not grounded. Lamps are 250V. One from each bus to physical "ground", thus 3 wires. Normally you see 125V across each one. During a "ground" event, voltage will be unbalanced. Note- the lamps are a low impedance and help hold the voltage balance. The voltage...

I know of one hydroelectric generator whose breaker failed to open when an unknown fault occured while shutting down for other service. Fault caused 86G lockout relay trip which turns off exciter & is supposed to trip breaker (energy storage device had failed). As unit did not complete its stop...

Thanks for all the input, guys. The end result is that for 750KW, converting the generator to 60Hz. is not practical or cost effective compared to a inverter.

In one brand they call it an electronic reversing switch as it switches which lead the cap is in. Not needed on a table saw.

I've seen electronic start switches in cable and chain hoists. If that fails, the motor will not start. They look like a capacitor, but aren't.

[glasses][glasses][glasses]If we needed to double the frequency, I could envision trying to install two layers of stator windings (so each pole was over two coils, not just one). But I don't see a way to do it for a 50% increase. Remove half the rotor poles & install three layers of stator...

There are 120 slots in the stator, 20 coils per phase. Single layer winding (makes it relatively easy to change coils when one fries.)

rasevskii, you are correct. The two freq. changers are still in operation. We have restored six units to full output, and would like to restore the seventh. Problem is, the changers can handle only 3 units each. Thus our search for a better way to make the conversion. As always, economics will...

The inverter is a good idea, but not economical for 750KW, 12KV, 40Hz input. Could put in a stepdown transformer, but not cheap for 40Hz.

The Francis wheel turbine chokes off water flow and will not rotate any faster than 140RPM, even at full gate no load, so speed cannot be increased. Rotor is cast iron, also cannot handle anything faster than that. No room for a gearbox (or its expense). We're familiar with re-poling the rotor...

We have a hydro powerhouse with 750KW 40Hz generators with 40 poles. We cannot increase the rotor speed to produce 60Hz. power. We have been told that the stator can be rewound to produce 60Hz. It seems like this would need 1.5 stator windings per rotor pole. There is only one winding per slot...

I am looking for a sensor to mount on a vented oil level sight gauge so that I may visually see the oil level and sense when it goes low (and maybe another one for high). Sensor could be a proximity type or an optical type. Most level switches are designed to be in a fixed location, and you...

We are already monitoring the secondary side through the generator protection relays (I didn't mention that this is a hydro plant with two generators). The transformer also has a tertiary 480V Wye winding for station service (does not have CTs). We'd like to know the difference between...

Unusual transfomer phasing question. 34.5KV/2400V Delta/Wye station stepdown transformer. CT's on the primary are connected wye. I need to use an existing multifunction relay connected to these CTs to monitor power consumption in the transformer, and so need primary voltage. I do not have PTs...

If a spot increases 6C above it's surrounding steel with just the test excitation it is a bad spot, will continue to get hotter as time goes on. With the 2000A drive it took 10 minutes to get the bad spots hot. It only took 5 minutes to start seeing the difference. Use judgement for what the...

The GPS samples each physical parameter 12 times per cycle, sample rate is adjusted to match measured frequency. But I suppose a really poor waveform could upset the process.

We had a stator core tested on a 750KW 120RPM generator, core is 10ft diameter. For the test a machine that could produce 2000A AC into a short circuit was brought in. Stator winding had been removed (damaged by a fire) so core was empty. Lead from tester was dropped into one slot, return lead...

Thanks to everyone who contributed to this thread. Everything seems to come back to it being a mechanical/water flow issue, not really an electrical problem.

Still doesn't answer why when troubled unit is only one on line it's power is stable. Adding one or two more units starts the problem. First time it was ever noticed unit B was fluctuating, unit A was stable. Either by itself was stable. Put C on with B, no problem. Put C on with A, problem...

We start back to back, synching at 60Hz. Then bring in the other two gen's at 40Hz. Generators are quite simple, no damper, one winding per slot, 120RPM. Generators are 12,000V nominal. Make 36A at rated power. Yes, we do try to run at 0 KVAR. Metering is a Basler GPS100.