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GE STD15C Instructions Manual

Transformer differential relays with percentage and harmonic restraint
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  • Page 2: Table Of Contents

    GEK-45307 CONTENTS PAGE ............ DESCRIPTION ............. APPLICATION ............. CALCULATION OF SETTINGS ......... METHOD ............ CURRENT TRANSFORMER CONNECTIONS ......DETERMINATION OF CT TURNS AND TYPE RELAY TAP SETTING . . CURRENT TRANSFORMER RATIO ERROR ......PERCENT SLOPE SETTING....? ....I DETERMINATION OF CT TURNS AND RELAY TAP SETTING ..

  • Page 3: Introduction

    GEK-45307 TRANSFORMER DIFFERENTIAL RELAYS PERCENTAGE AND HARMONIC RESTRAINT INTRODUCTION Relays of the STD type are transformer differential relays provided with the features of percentage restraint. A static decision unit controls a small telephone type relay Percentage restraint permits accurate discrimination between internal and external faults high while harmonic restraint enables the relay to distinguish, by the between...

  • Page 4: Current Transformer Ratio Error

    100% Transformer KVA (Line KY) Actually this calculation does not mean that all windings will necessarily carry these load currents continuously. This is only convenient of calculating the currents in other windings In proportion to their voltage ratings. This is the requirement for selecting the relay tap setting so that the relay will not operate for any external fault.

  • Page 5: Percent Slope Setting

    Determine burden on each CT. using the following expressions: connected CT's b. For delta CT'S relay total burden (sea Table number of turns in bushing CT (at maximum bushing CT resistance per turn, CT resistance per lead. temperature) control cable lead expected temperature) current for 8 times tap setting.

  • Page 6: Std Relay Tap Setting

    REFER TO FIG. I DETERMINATION OF C.T. TURNS AN0 RELAY TAP 1. Transformer and Line Ip = (line 3 ( l i n e turns 5. Max. I secondary (less than 2.62 6. 100% I secondary CT connections Relay Current for 1002 I Sec. 1.37 1.98 3.60...

  • Page 7: Ia Repeat-Ct Turns And Relay Tap Setting

    1.085 0.833 36.8 69.6 27.8 29.b 58.0 ES CT required required, excitation curve 1.00 3.4% 136% Ratio Error high; should try higher tap on CT to improve CT Exciting current on line IA REPEAT CT TURNS AND RELAY TAP SETTING 15.7 39.6 Try CT turns (necessary to change C...

  • Page 8: Auxiliary Relay Control Circuit

    amperes for second measured in the primary Of any nigher may be applied for shorter lengths of time in accordance where: current amperes time in seconds Of the multiples Of tap Short Time (electrical) to the relay from the several sets of current transformers should not exceed 150. These multiples should This limitation is a result of the voltage be calculated on the basis of fault current.

  • Page 9: Through Current Restraint Circuit

    It should be recognized that pickup current flows not only through current transformer but also through one of the primary windings of the through current restraint. However, compared to the operating energy, this quantity of restraint is so small it may assumed to be zero.

  • Page 10: Case

    OPERATING UNIT The primary functioning of the relay is a state amplifier whose controls a simple telephone relay. The sense ampllfler is shown In Fig. 10 and as a large rectangle. The amplifier consists of many electronic components mounted on a printed circuit card in the top half of the relay. This printed card is installed in an eight-prong printed card design base.

  • Page 11: Acceptance Tests

    ACCEPTANCE TESTS the relay an inspection and acceptance test to insure that the relay has not been and that the relay calibrations are unchanged. VISUAL INSPECTION Check the nameplate stamping insure that the model number. rating and calibration range of relay received agree with the Remove the relay from its case and chock by visual Inspection that there are no broken cracked...
  • Page 12 of a voltage across studs 8 and 9 This curve represents the relay characteristic. which is 75: or less of the value given on the curve does not necessarily indicate that This is especially true where very high through operate at higher through current cause CT saturation.
  • Page 13 C K U P pickup is as described under the heading INSTALLATION current be different depending upon the UDG Pickup value be determined as 0 . 3 0 1 T a p IO percent variation Still course, when pickup on a particular service the acceptable as found values being 0.30 Tap to 1.10...
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  • Page 15: Pickup

    INSTALLATION PROCEDURE TESTS , check the relay calibration to be used in its final location Before placing the relays I" The following test procedure is outlined for this purpose. to insure that It Is correct. CAUTION: RELAY CALIBRATION IS ACCOMPLISHED BY ADJUSTING RESISTORS R IN ANY ONE THESE RESISTORS WILL AFFECT THE OTHER TWO SETTINGS.

  • Page 16: Through Current Restraint

    of adjustment. it be corrected by adjusting Rheostat If harmonic restraint is found to be THROUGH CURRENT The through current restraint. which gives the relay the percentage differential or percent slope It may be checked and adjusted using the circuit illustrated in Fig. characteristics are in Fig.

  • Page 17: Connections

    CONNECTIONS Internal connection diagrams are shown in Figs. 10 and 11. Typical wiring diagrams are given in Figs. 7. 8 and g for differential applications. Of course, any through current winding may used for any provided the taps are properly chosen. the relay is mounted on an insulating panel, one of the supporting studs should be cntly grounded by a conductor not less than No.

  • Page 18: Percent Slope Setting

    voltage across studs 8 and g This curve represents the relay characteristic. which or' less of the value given on the curve does not necessarily indicate that will This is especially true where very high through faults My operate at higher through current values. cause CT saturation.
  • Page 19 method checking pickup is as described under the heading INSTALLATION Pickup value may be determined as current will be different depending upon the 1 T a p 0.30 when a particular service tap, the percent as found values being 0.90 0.30 1 Tap 1 .
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  • Page 21 OPERATING SPEED CHARACTERISTICS OF THE RELAY F I G . 3 ( K - 6 2 0 9 1 9 5 - 0 ) Courtesy of NationalSwitchgear.com...
  • Page 22 RELAY TYPE CASE, APPROX (LEFT (8042544) RELAY TYPE CASE, APPROX (RIGHT Courtesy of NationalSwitchgear.com...
  • Page 23 FIG. 7 (012881981-l) ELEMENTARY DIAGRAM FOR RELAYS FOR TRANSFORMER PROTECTION Courtesy of NationalSwitchgear.com...
  • Page 24 500n 500n FIG. INTERNAL DIAGRAM FOR RELAY TYPE Courtesy of NationalSwitchgear.com...
  • Page 25 RELAY RELAY FIG. 12 (016582697-O) TEST CONNECTIONS Courtesy of NationalSwitchgear.com...
  • Page 26 Courtesy of NationalSwitchgear.com...
  • Page 27 COOLED AIR COOLED FIG. 17 USED IN SAMPLE CALCULATIONS SENSE PRINTED CIRCUIT INTERNAL CDNNECTIW Courtesy of NationalSwitchgear.com...

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Std16c

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