50 hz ammeter on 60 hz circuit

[JW 569]

I am retrofitting controls on a 4160v starter. I found that there was a CT rated at 600v, 60 hz, 200:5, around a 5kv unshielded cable, with the secondary connected to an ammeter rated at 5a f.s., 50 hz (this is a 60 hz system). While I have reservations about the CT, I can install an insulation sleeve over the cable to reduce the possibility of line potential getting to the meter.

My real question is about the meter. Is it safe or accurate at 60 hz? My opinion is that it is only as safe as the CT, but I'm not sure how, or if, frequency affects the accuracy.

If the meter is an issue, I can go to the customer and justify replacing the CT and the meter.

 

[gar]

130315-1115 EDT

JW 569:

My guess is that there should be no significant accuracy problems.

What would be the source of a problem? There is little difference in frequency. Slightly more core loss. Should not be a saturation problem. Relatively there is more damping of the meter movement. Possibly slightly higher losses in the meter.

Add your insulation and try it. There should be no great problem. Use an independent means to check the calibration.

.

 

[Besoeker]

I am retrofitting controls on a 4160v starter. I found that there was a CT rated at 600v, 60 hz, 200:5, around a 5kv unshielded cable, with the secondary connected to an ammeter rated at 5a f.s., 50 hz (this is a 60 hz system). While I have reservations about the CT, I can install an insulation sleeve over the cable to reduce the possibility of line potential getting to the meter.

My real question is about the meter. Is it safe or accurate at 60 hz? My opinion is that it is only as safe as the CT, but I'm not sure how, or if, frequency affects the accuracy.

If the meter is an issue, I can go to the customer and justify replacing the CT and the meter.

FWIW I'm from the UK.
The CT's we used are suitable for 50Hz or 60Hz. I think most are. The meter you have is most likely moving iron which responds to I_rms so should not be affected by frequency.

 

[Besoeker]

Just to add to the previous post, this a section of the ACCT specification from our incumbent supplier:

 

[jumper]

ammeter rated at 5a f.s

What does this mean? 5 amps? 5%? Of what?

 

[USMC1302]

Just a guess, but maybe f.s. is "full scale"?

 

[USMC1302]

Try this again, maybe f.s. is full scale?

 

[SG-1]

What does this mean? 5 amps? 5%? Of what?

The ammeter input is from a 200:5 CT. 200 amperes in 5 amperes out. The ammeter pointer with 5 amps flowing reads full scale on the faceplate. The faceplate is marked or scaled, so the reading is matched to the CT output. This is also called ES or End Scale. The ammeter reads 200 amperes, but only 5 amperes is flowing through it. If it were reading 100A, then 2.5 amperes would be flowing through it.

 

[Phil Corso]

JW 569...

Just a general note about CT accuracy! Of course, a CT is affected by frequency! Doesn't its Emf depend on f?

Emf = a bunch of numbers x f x Cos(more numbers x f). Thus, accuracy is certainly affected!

Now, “the good-bad story!” 'Bad' means accuracy worsens as frequency decreases! 'Good' means accuracy improves as frequency increases!

I believe that a similarr concluston can be made about the ammeter! But, to be practical, the difference between 50 and 60Hz is inconsequential!

Regards, Phil Corso

 

[Besoeker]

Just a general note about CT accuracy! Of course, a CT is affected by frequency!

Did you not read the manufacturer's specification?
Look at the bit about frequency range. I believe that deals directly and succinctly with the OP's query.