Unable to Measure Frequency in One Phase


Thread Starter


Dear All,

We deliver the generator (380 V/50 Hz/ 3 phase) today. We are not able to measure the Hz in one of the phase during test run. We can only measure on Phase 1 and 3. But we can measure voltage in all 3 phase. What is the root of cause and how can we solve?

The alternator brand was Stamford.


If the Generator is "Y" connected, then absence of an Hz measurement indicates that Leg of the "Y" is disconnected... perhaps at the terminal block!

What are the three Line-Line, three Line-Neutral, and three Line-Earth, voltage measurements?

Phil Corso

There is most likely something wrong with your measurement method. Please review the electrical schematic drawings provided with the generator and the relaying and metering equipment (in particular, the potential (voltage) transformers) and be sure you can measure all three phases of frequency. If the voltmeter you used is a multimeter capable of measuring frequency as well as AC voltage, then it should be possible to measure the three phases directly--not through potential transformers (presuming the meter is rated for at least 380 VAC; most industrial multimeters are rated for 600 VAC, some more).

But, it's pretty certain that either there's something wrong with the measurement procedure or the terminals where the frequency measurements are being taken, or there is some physical connection/termination problem.

Please review all generator winding terminations (high voltage connections), and all potential (voltage metering and -relaying) transformer connections. And, again--if your meter is properly rated, it should be possible to measure each phase's frequency directly (with appropriate precautions/safety equipment).

And, please write back to let us know what you find!
Dear All,

Thank you very much for your help and advise. Next day, we can measure the HZ but it is too much. So we check all devices and try one after another. We found out that the (3) metering device was sensitive enough to measure the electronic noise. We get the right HZ after using the analog meter to measure.
Really? Someone gave an Unhelpful vote for thanking the original poster for providing feedback on the problem resolution?


That's just sad; really sad.

<b>Moderator's Note:</b> I'm hoping they selected the wrong thumb by accident.