Checking Phase Sequence

[electricuwe]

I'm searching for a device suitable for checking the phase sequence on ungrounded three phase systems up to a voltage of 750 V or higher.

The devices easily availbable only work on grounded systems (Two terminal devices like the DUSPOL from Benning) and the three terminal devices I found are limited to lower voltages.

Since there is no simple instrument available we often have to check phase sequence with an scope and high voltage probes.

 

[busbar]

e-u, could you describe the high-voltage probes used for this?

 

[nbucska]

E-mail me. <nbucska@pcperipherals.com>

 

[jbartos]

Suggestion: Visit

http://www.thomasregister.com

and type Indicators: Phase Sequence under Product or Services, which will return 22 Companies to contact regarding your special needs, e.g. Eastern Specialty Co.

 

[electricuwe]

To busbar

we usually use two 100 : 1 Probe e.g. from Gould and connect them for differential to the the scope for differential measurement. For reference the scope is set to line trigger so that checking phase sequence is possible by measuring one phase to phase voltage at a time.

Unfortunately the Gould probe we use are not availbale any longer.

An alternative is to use a differential probe from pewatron.

 

[230842]

Are you ready to construct your own home-made phase sequence tester? all what you need is two resistors, one capacitor and a simple multimeter (able to meassure line voltage). If you are interested let me know and I´ll mail a simple scheme. Device operates on three lines without neutral. Julian

 

[electricuwe]

Julian,

I think I'm able to built a phase sequence tester myself but I would like to find a source for a device which is manufactured industrially and tested for safety so that I can hand it to our commissioning engineers without worrying about their safety.

We have to check the phase sequence on the secondary side of transformers rated several MVA. Using a device like the 'simple multimeter' may be extremly dangerous, not mainly due to voltage but due to arcing if the device is defective or set to current or resistance measurement.

I personally only use multimeters including a fuse with high beaking capability (100 kA) for that purpose.

 

[busbar]

electricuwe, thank you for the followup description. Please allow me to suggest that it may be desirable to verify that the probe manufacturer and supplier intends for his product to be used for direct connection to AC-power circuits.

The devices that contact utility or industrial power circuits should be intended and clearly identified as “power-class” instruments and instrument accessories. It is routine to anticipate relatively high short-circuit currents and transient overvoltages in 50-60Hz power circuits.

Although they may be seem to be OK used within labeled maximum voltage, this type of probe may not be intended for application to power systems. Verify that they are specifically intended by the manufacturer for direct connection to AC power circuits. It is reasonable to request for published evidence of these ratings if there is any question on the subject.

The generally accepted “industry norm” for ~2.3-5kV ø-ø circuits, AC power distribution equipment is rating of 60kV to 95kV Basic Impulse Level {withstand, impulse/transient overvoltage.} Generally accepted “industry norm” for <15kV ø-ø circuits is a rating of 110kV Basic Impulse Level {withstand, impulse/transient overvoltage.} ‘Creep’ and ‘strike’ clearances on power components {across insulating surfaces and through the air} are designed and rated corresponding to accepted BIL values.

There are “generally recognized as safe” methods for measurement of medium-voltage electrical characteristics. That the circuit under test is acknowledged as ungrounded adds some additional considerations for applying test equipment.

If for any reason you would like to correspond outside of the forum: busbar@@pacbell.net

 

[electricpete]

Possibly not relevant... but often the verification can be made by checking voltage across open contacts of open switch/breaker connecting to a source known to be of proper phase sequence.

 

[busbar]

10-4 good buddy electricpete! A phasing voltmeter set [~<69kV] was to be my next suggestion if tie circuits were available or the circuits were in proximity of each other. electricuwe, that's how it's routinely done, and usually provisions are engineered into distribution systems for this capability. The spacing between the busses of interest is limited to ~20 feet, but there are relatively safe instruments to do this—usually mounted on plain-vanilla 100kV/ft hotsticks. An open tie switch/breaker is ideal for this.

Could you respond with the min-max voltages you are working with, electricuwe?

 

[electricuwe]

busbar,

Usually the incoming voltages we use in our equipment are limited to 750 V, in some case voltages up to 1200 V may be used. I guess thats to low for using medium voltage equipment.

I'm aware that for multimeters there is a standard, IEC61010 deviding the applications into 4 different categories depending on fault level an voltage surge level.
Our application would be comparable to CAT IV.

The big advantage of using an oscilloscope probe is that in a probe the large resistance of the voltage divider is located in the tip. So, as long as this resistor isn't damaged by an overvoltage, it limits the fault level on the cable to the scope significantly. Since we use differential measurement, both lines are protected that way.

Unfortunately suitable probes are quite rare, the probes available either have not an suitable voltage rating, the cable is to short or the tip is made for connection to an IC-pin and not to a busbar of 10mm thickness. So sources for suitable probes are also welcomed.

 

[busbar]

e-u... I recently found a phase-sequence tester advertised online that [I think] had a 2500-volt rating, but I cant find it at the moment. It seemed like it was intended for some out-of-the-ordinary function or made by a specialty company; vaguely like “Fred Garvin’s Benzene Pump Gasket and Lefthand Fillister-Head Screw Supply.” The device had heavier-than-usual leads on fairly big Mueller clips with stock boots. I ‘m fairly sure it did not carry any sort of IEC1010-1 (or anything like that) rating, but it looked fairly stout; in a plain black bakelite box with posssibly a yellow-faced front/label. It may have been the “five neon lite” type. The features made it look like it could have been designed 30 years ago.

I’ve searched on ‘phase—sequence/rotation—meter/tester/indicator’ and the same few basic styles seem to be listed everywhere.

I'll keep looking. It’s gotta be out there somewhere. I think the maker was in Texas.

 

[busbar]

There’s this but it seems to have an odd limitation…

http://www.stbinc.com/products/rotation/50109G.html

“The Model 50109-G-02 [model 560-5] operates on a frequency range of 60 Hertz with a voltage range intended for 4160 volts to determine sequence in polyphase circuits.” BUT, according to the guy that assembles and tests them at STB, the leads are rated for 1kV and the WHITE lead is intended to be connected only to a *grounded neutral* 4w wye distribution system.

So, apparently that model is NOT intended to be connected to an ungrounded {3w delta} system; only two phases and neutral of a GROUNDED-WYE system.

(Of topic a bit, but STB also makes phasing voltmeters that are used to compare phasing [not phase sequence] like

http://www.stbinc.com/products/volt/25_35.html

)

 

[busbar]

electricuwe, would you send me a pvt email at: busbar@@pacbell.net ? [note munging]