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We have a distribution system which, with some active harmonic filters, can be made to meet all of the harmonics limits of IEC61000.2.4 (Class 2) & IEC61000.3.6. When the negative phase sequence components of voltage are geometrically added, however, we get a negative phase sequence voltage 2...

I have been caught specifying P class CTs for differential schemes which have turned out not to be adequate. Now, I specify PX class wherever it is possible to do so. The problem with P class is that you have no control over the winding resistance which is critical to the onset and severity of...

Schneider make new Low Power VTs for use in their MV Switchgear. They can work up to 20 kV and have an output of 3.25/root 3 volts. Does anyone have information on how to integrate them with a SEL751 relay with LEA RJ-45 inputs? What kind of cable is needed and what length & method of...

My Dear History Buffs, Many thanks for the replies. All of them are engaging and educational. Dear Waross, Would you kindly confirm that the rotary converter's winding, or windings if polyphase, are common to both the AC and DC circuits? Dear dArsonval, I am sure I will find my 'DC Balancer' in...

Dear Heritage Buffs, I am reading a report from 1912 in which the author is comparing rotary converters with motor-generator sets for the conversion of 440 V AC to 600 V DC for tramways use. Can you please explain the difference? In another report the DC power stations of that time are said to...

Folks, Thank you for your questions which are answered below. The earth fault current is measured from the residual connection of the three phase CTs which is fed into the "Ground" input of a type SR750 relay. The three phase CTs are installed on the bushings of a Schneider type YSF6 circuit...

Folks, thread238-447179 posted 10 Dec 2018 asked about relay behaviour when protection CTs were double earthed. Some testing at site has confirmed that there is a single earth reference for the CT secondary circuit. The CT earht5ing was not, therefore, responsible for the nuisance earth fault...

Waross, Thank you. We shall try to tong test the CT neutral - earth wire to see if anything is flowing in it. That should be possible for our testing people.

We have a three phase overcurrent plus earth fault relay installed on a bus tie breaker in which the earth fault element is fed from the residual connection of the three phase circuits. The CTs are IEC P class 1200/1 A. Recently, when the circuit was passing 700 A, the relay tripped on earth...

Folks, Below are the events for the day in question: FID = SEL-710-R410-V0-Z006004-D20140303 CID = 9A42 # DATE TIME ELEMENT STATE 52 08/02/2018 17:06:18.923 IN407=CB READY (TO RACK) Deasserted 53 08/02/2018 17:01:59.333...

Hi Scotty, Injection tests were conducted several weeks prior to final commissioning. The Blower is running now with the next window of opportunity for testing being 12 months away. I still don't have any SoE from the relay but believe it is coming tomorrow. Right now, my client is quite happy...

Scotty, The operators stopped the running motor from the relay panel and the engineer who was present did not notice any flags on the relay. A short time later, after the operators had racked out the CB truck, he noticed the earth fault LED. The cable cores were meggered and found to be in good...

Thank you for the valuable feedback. For your information it is a DOL starter incorporating an ABB type VM1 vacuum circuit breaker. In the attached zip file are: 1. the trace that was omitted in error from the original post, 2. the AC schematic, 3. a photo of the cable termination...

This induction motor has been running successfully for many years on a 3.3 kV switchboard which has become obsolete. It was re-connected to a new 3.3 kV switchboard and the following observed immediately after completion of a successful bump test. What was different about this bump test is that...

Could someone please explain what value of resistance should be used in the plant impedance parameters when calculating the DC component of breaking current using the IEC60909 methodology for maximum short circuit current calculations. I understand the temperature should be at 20°C but I do not...

Thank you, Z. The ANSI standard Referred to is IEEE 0242-2001 (Buff Book) and Table 15-3 gives 'minimum' CTIs for various combinations of protective devices. My concern is grading with an upstream relay.

Under what circumstances will a current limiting fuses take longer than one half of a power frequency cycle to fully interrupt a short circuit current significantly greater than the current at which the fuse begins to current limit? Are there differing considerations for HV fuses versus LV...

In order to calculate the longest fault clearance times permissible in an industrial power system I need 'stored energy constants' or H factors (in seconds) for the turboalternators. All machines are powered by 8,000 rpm steam turbines via gearboxes. These turbines are pass-out or non-condensing...

Are there examples of either industrial or utility MV (approximately 1 to 33 kV) distribution systems operating without any form of system earth. By any form I exclude even voltage transformer earthing. I mean fully floating.

Dear readers Can any of you convert the following CT specification into an IEC specification(IEC is first preference but ANSI would also be helpful) :- Westinghouse EPGH Current Transformer RCT-9 S#300P596G01 Current Ratio 1200:5 L559852-C 60CPS The CTs must be around 40 years old.