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  • Users: Vegemite
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  1. Vegemite

    IEC60034.1 and NPS Voltage

    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...
  2. Vegemite

    Schneider LPVT

    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...
  3. Vegemite

    Heritage: Early 20th century power generation

    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...
  4. Vegemite

    Mutual Coupling between single core cables on same ladder

    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...
  5. Vegemite

    Double Earthing of CT Circuits

    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...
  6. Vegemite

    Coasting Induction Motor Trips when supply CB open

    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...
  7. Vegemite

    Short circuit studies to IEC60909

    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...
  8. Vegemite

    Current limiting fuses

    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...
  9. Vegemite

    Machine Dynamics: H factors

    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...
  10. Vegemite

    MV System Earthing

    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.
  11. Vegemite

    Old spec for a CT

    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.
  12. Vegemite

    Induction Motor Short Circuit Current

    Given the following resistance and reactance values how can we work out the magnitude and power factor of the three phase short circuit current for a fault near to the motor terminals. The givens are per unit values of:- -stator (R1, X1) -rotor running values at rated speed (R2, X2 at slip ~...
  13. Vegemite

    Hot/Cold ratio

    I am trying to protect an 11 kV, 50 Hz, 2 MW, Alstom Cegelec squirrel cage induction motor built to IEC standards with an electronic motor protection relay which wants the hot/cold ratio entered. I know the motor is rated for 2 cold starts and 1 hot start, has a thermal time constant of 33...
  14. Vegemite

    Distance Protection with Zero Ph. Sequence Throttling

    There is this radial 132 kV line which is part of a solidly earthed transmission network. It is a teed radial line thus: - source = substation A - tee point = T located 16 km from A - first load substation = B is 0.6 km from T - second load substation = C is 8.5 km from T. There is no generation...
  15. Vegemite

    Transmission Line Zero Phase Sequence Impedance

    In Australia there are large salt lakes. I am modelling a transmission line which runs on a low causeway built through the middle of one. Does any one have measured or calculated values of earth resistivity for such an environment. Values in Ohm metre are prefered.
  16. Vegemite

    T60 Universal Relay Transformer Protection Relay

    Does anyone have practical experience with the T60. Are the main biassed differential elements and the restricted ground fault protection elements stable for energisation and through faults?

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