Essential-Service Motor Defeating some important motor protection ? 4

[sparky1976]

Hello every body,

I have problems with my motor protection lots of them, often false tripping and no cause found try hundred times to to trouble shot or probably incorrect settings but everything seem OK.
When I found technical paper from GE chapter 10 A-C Generator and motor protection on page 202 its rather confuse me its seem the motor is poorly protected, is it a usual pratice ?

If I want to disable the 46 that protect motor from single phasing trip, is there someone can advise me the brand that sell single function 46 device (the relay I got is one package) or is it safe enough and leave it to thermal as back up?

 

[peterb]

Further to what Electricpete (and Busbar) have mentioned, it would be really helpful to know whether the relays in use have any event/oscillograph recording capability and whether they have been giving any data on the trips. An amazing amount of detailed information is available from some relays - I fully endorse what Electricpete had to say on SEL's capabilities, based on extensive use of their various products on transmission and distribution systems.

In fact, it if the relays do not have this capability, it would be worthwhile to install a temporary "recording" relay in series to capture event data - trigger this relay recording from a trip output of the in-service relay. This will give a good handle as to whether the problem is in the relay or is a valid response to actual system conditions. I have used this technique with great results on distribution systems to unravel really obscure system operational problems.

 

[BJC]

Very good suggestions on the last two post. It could be expensive and take a while to build a data collection system for the system. There are PC based systems that will do it. If I were going to do something like it again I would start with Action Instruments or something similar. I would also record or monitor system parameters like damper positions, starting and stopping of other fans, flow ( paddle switches would work ).
I would suggest for starters he have operations ( of whoever runs things ) log their activities ( all of them). The cause and soultion might be apparent after some analysis.
There was an "industrial legend" about a power plant that shut down whenever a certain toilet was flushed. It went something like it was lowering pressure to a sealwater line, which tripped a feed water pump which tripped a boiler etc.

 

[jbartos]

Suggestion: Visit

http://www.tde.alstom.com/p-c/en/papers.htm

for a paper:
May 2000
"Distributed Intelligence in Integrated Substation Protection and Control Systems"
Dr. A Apostolov

 

[sparky1976]

Guys, tanks for your response,
First thing I do is check all the wiring to meet vendor standard on their instruction book. All grounding point are correct for the relay and instrument transformer.
The common thing to all relay that I can think of is DC power supply and grounding. DC fluctuation 0,5 V from 130 VDC, and grounding resistance less than 1 ohm.

The fault occurs after the motors runs for days or months, and suddenly just trip.

Yes my relay can capture wave form and event data when fault occurs.

Here one of my waveform:
VT input for the relay is open delta.
the target was undervoltage trip. when I see the waveform capture Va is in-phase with Vc with no reduce in magnitude
and the VT is common to another 7 relay and only one that act like that,and this problem is always changing to another relay.

Is anyone ever see a fault record and the one voltage wave shifting 120 degrees to be in-phase to another another voltage.

 

[electricpete]

Never saw anything like that. But if you got an undervoltage trip and anomolous indication for voltage then you need to troubleshoot and understand the voltage input some more (sorry if that was obvious).

There are lots of possibilities. One that comes to mind is an intermittent open circuit in your PT circuit. I saw that once caused by intermittent contact at the fuse ferrules in the PT secondary. Also some potential transformers have draw-out feature which automatically disconnects primary and secondary circuits when the PT is pulled out... a good spot for an open circuit.

I'm not sure I 100% understood your voltage input circuit (open delta on primary or secondary side of the CT's?.. and what setup on the other side). In any event it seems REMOTELY possible that for an ungrounded power system with a grounded-wye primary-side PT, a momentary ground on the power system would cause the PTs to sense zero voltage on one phase.

 

[electricpete]

Troubleshooting for an open ciruit do continuity checks on the primary and secondary circuits (as much of the circuit as possible). Try banging the equipment a little to see if you can cause an open circuit.

Is there perhaps two different secondary windings on the same PT? Maybe that explains why one motor tripped and not the other?

 

[BJC]

What kind of DC powere supply do you have?? Is it totally isolate? By Isolated I mean neither side is grounded (floating). In the situations I know of there would be two wires on the DC system and measuring either of them to ground would result in a 0 (zero)volt reading. Measuring between the wires gets a reading of 125 v DC.
That is unless there is a device connected to the system that has an internal ground connection. that device may have a direct connection to ground or through a resistance of some value.
The device may not be connected to the DC system all the time or may operate intermittantly. This may or may not be related to the tripping problem.
Grounds or partial grounds) in DC systems are sometimes hard to find. Ths last one I tracked down was in the electronics of an annunciator system. The DC system would read -30 and +90 volts to ground.
I still think logging and monitoring ALL events will help. Make sure you have complet schematics (protection, control, computer inputs, and interlocking controls to other equipment) of the fan control circuits as well as everthing connected to your DC buss. Correlate any event you can with a trip and investingate the schematics for system involved with that action. Look for thing that can generate a trip signal.

 

[busbar]

A pair of PTs (VTs) can be used in switchgear with high sides connected phase to phase, most often in an open-delta configuration tapped from a MV bus through three (or sometimes four) current-limiting fuses. To accurately reflect primary phase-to-phase conditions, the secondaries are almost always connected in the same open-delta arrangement. To prevent electrostatically-induced overvoltage on secondary equipment, the winding pair is corner grounded, (and, mentioned by others here, at one point only) with fuses (often 1-6 amp) only in the two ungrounded secondary conductors. [ANSI/IEEE C57.13.3 §2.6.1] The PT arrangement will essentially ignore phase-to-ground voltages (a/k/a ‘neutral shift’) on the serving bus, which is acceptable where there are only 3-wire motor loads. It seems customary to connect PT secondaires to limit voltage to 150 to ground, and/or 150 volts between conductors.

But to recap a bit, the original posting discussed negative-sequence overcurrent (46) trips as the culprit—but recently undervoltage (27) [or possibly 47/negative-sequence voltage] operations are stated as taking motors offline. It is typical for these voltage elements be configured with definite-/inverse-time tripping characteristics. Is it possible that seemingly random nuisance trips are the result of ‘hare-trigger’ settings?

Part of the troubleshooting process should cover well-studied ruleouts if unlikely causes, such as CTs with unmatched kneepoints or auxiliary DC transients, causing relay packages to assert falsely. [See

http://www.pes-psrc.org.

. . thanks, Charlie H.]

Electricpete, you raise an interesting point—how about temporarily loading the PT secondaries to eliminate PT/fuse/connection problems? Two or three 60-watt lamps at the various relay-package terminals would likely do it. Don’t most MV PTs have thermal ratings of 500VA or better?

I think readers will be very interested in your resolution to such a frustrating problem.

 

[sparky1976]

Guys,
Here one wavecaptured from false fault recently occured.
target single phasing trip but the fault recorder still record Ia, Ib and Ic. But Ia shifted to in phase with Ic.

I think if single phasing trip one of the current should be zero.
We check and try to start the motor running and still running till now.
I've done a lot of thinking, I have one substation with the same cofiguration (I mean CT's, PT's and relay setting, that I recall never trip.
One of the unique of this substation is the relay donot send data to DCS using rs485.

Is it any possibility the relay that send the data Its Processor "exhausted" and want a rest for alittle while ?

 

[peterb]

Yamin, please advise some details of your electrical system configuration -
- What is the operating voltage of the motors?
- Is the motor distribution system wye or delta? 3-wire or 4-wire?
- What is the winding configuration of the transformer feeding the motor substation? Wye/delta? Delta/wye? Delta/Delta? (also advise vector group)
- What type of neutral grounding is used? (Both HV & LV systems)
- What type of switchgear feeds the transformer HV? Are there fuses involved?
- Are the motors wye or delta connected? Is there any other delta connected load?

The phase current will not necessarily be zero for a case of single phasing, if the single phasing is on the HV side of the supply transformer. The clue to this problem may very well lie in the recordings - more to follow after you provide the above info, as I can see at least one scenario that may explain your recordings.

 

[electricpete]

Just thinking out loud some more.

On one occasion your relay saw a loss of one phase of voltage. On another occasion (or possibly same occasion?), your relay saw a loss of current.

Assuming the above two observations originated from a single common cause eliminates a lot of the possible causes I mentioned: couldn't be a problem in PT circuit (wouldnt affect current). Likewise couldnt be a problem in CT circuit (wouldn't affect voltage).

It seems like only two types of causes are left:
#1 - The relay is deranged for some reason (power supply/emi noise problems, dcs communications, beta version of the software etc).
OR
#2 - Your motors are seeing an actual single-phasing condition due to loss of voltage or open circuit at some point in the supply (upstream of the PT location). Since the problem is reported in many different motors it would likely have to be point upstream/common to all of the motors (near to your incoming power). It seems relatively unlikely that momentary single-phase power interruptions could occur repeatedly without you getting other indications... but possibly worth some monitoring or discussion with your utility company if you don't turn up anything else with the relay.

 

pleas send for me total of products
tunk you very mutch

 

[sparky1976]

Peterb
Here's the illustration of my system

I have a transformer 11kV/3,3kV Dyn1. The 3,3kV has NGR 200 A. This XFMR feeds a MV MCC. This MCC feeds motors (7 motors) that starts direct on line.
The bus PT's (that connected open delta, the 'B' phase on secondary grounded)act as common PT to all relays on the MCC.
All the motors are star.3 wire connection.
I have 4 substation typical to what I illustrate above.

So if the PT did some thing funny it will affect all the relays, does it ?
And the single phasing trip will read 2 phases only not 3 phases currect since the motor starts DOL ?

I'm still confuse, because the wave from fault recorder is not match any theory that told in school or books ?

 

[busbar]

Do all relays connected to the common set of PTs show the same problem in their fault reports? ...at the same time?

Does the relay manufacturer have any applications-support people with which you can review the reports?

 

[jbartos]

Suggestion to yamin:
1. Please, provide info Peter have asked for, since it is needed to arrive to some reasonable solutions.
2. Specifically, the power transformer connections and system grounding are needed.
3. Also, the power transformer upstream connections and grounding schemes.