coils overview rev2

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1 Coils for ACB C&S Proprietary, Duplication Permission Required FUNCTION: • CLOSING COIL - CLOSING the ACB from remote SHUNT TRIP COIL - TRIPPING the ACB from remote UNDERVOLTAGE COIL - TRIPPING the ACB when system voltage dips or vanishes ADDITIONAL FUNCTIONS: • CLOSING COIL – Anti-pumping* SHUNT TRIP COIL – Interlocking UNDERVOLTAGE COIL – Interlocking, though not recommended *

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Page 1: Coils overview rev2

1

Coils for ACB

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FUNCTION:

• CLOSING COIL - CLOSING the ACB from remote

• SHUNT TRIP COIL - TRIPPING the ACB from remote

• UNDERVOLTAGE COIL - TRIPPING the ACB when system voltage dips or vanishes

ADDITIONAL FUNCTIONS:

• CLOSING COIL – Anti-pumping*

• SHUNT TRIP COIL – Interlocking

• UNDERVOLTAGE COIL – Interlocking, though not recommended

*

Page 2: Coils overview rev2

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Coils for ACB

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MECHANICAL PART

Snap-fit spring

Pole piece 1

Coil 1

St.steel plunger

Coil 2

Pole piece 2

Armature(moving core)

Non-magnetic spacer

St. steel Return Spring

Electronics

Yoke

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Coils for ACB

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TRAVEL

Travel in all coils is 9 mm

Constructional difference between CC/ST and UV

Page 4: Coils overview rev2

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Coils for ACB

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ELECTRICAL PART

COILWhy two coils ?

For pickup, we require a high ATFor holding, we require much less

Why not for Closing coil ?

It does not need to hold on. It should operate once and come back. About 200 ms ON

Why ?

Electrical anti-pumpingLength of mean turn

= * (15 + 6) (allowing 0.5mm for tape)

= * 21 = 65.97 mm

Lm * No of turns = Total length of wire

32 20

6.5

15Dm

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Coils for ACB

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Design

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Coils for ACB

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Design – continued ..

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Coils for ACB

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Design – continued ..

Steps :

1. What is the force required ?a) To pick up –b) To hold –

Ampere turns to develop the force… how to calculate ? Very difficult.. So? Trial and error to establish what will work

2. Having established the AT required for pickup and hold…a) Try various gauges of wire to see which ones work.*b) Wind the coilsc) Test them aloned) Then with electronicse) Then with ACBf) Then for cyclic performanceg) Then for continuous heat-run

* see the slide after the next one for explanation Simple isn’t it ?

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Coils for ACB

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Not quite !

Let us take this one – 220V UV Coil• Original was OK, but running a bit hot• So we tried the next smaller wire – Temp rise OK, but too weak to hold 2 kg spring• One size larger, holding OK, but ran even hotter. So what option do we have ? NOT MUCH !• So decided to cram EVEN MORE turns of 46 SWG. Even at the risk of bulging. Worked OK

• Winding tension (32 g) absolutely important … • If too low, winding will bulge beyond limits• If too high, wire will stretch, thin down, and resistance will go haywire. So must be wound at TC with lots of care

• If this gives a problem still, what to do ?• try to make the 2 kg requirement less. Ie., make the trip system of ACB smoother.•Then we can use say 1.2 kg spring, and then the 47 SWG coil may be OK …

see what I mean ?

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Coils for ACB

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Design – continued ..• Put in wire values –

• bare wire dia for resistance calculation• over-enamel dia (gr 1 or 2) for max turns calculation

• calculate area values for both• take 84% winding factor and calculate number of turns accommodatable• calculate resistance• divide V by R to get current value, hence get AT, VA• iterate all above for different wire gauges to get different coil data

you can then get peripheral useful data like adiabatic 1 sec temp rise, weight etc

Things you should know : • Coil design is based on 1.68 cm resistivity of copper which is true for annealed copper

@ 20o C. Due to work-hardening, and some other reasons, it can go up to 1.73 cm

• When coil resistance is measured, the ambient temperature must be noted, and a correction factor applied. This factor is 0.00393 / oC

• IEC specifies E8% tolerance on resistance per meter of Copper wire• Coil resistance must be measured using the resistance method. A calculator is available.

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Coils for ACB

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Design – continued ..Design guide: Closing coilCoil is intrinsically DC operated If customer applies AC or DC, it will go through a rectifier bridge (can be SCR bridge), so that the coil only sees DC.The coil can be only one, with enough amp-turns to operate the plunger.Simple electronics – feeds the coil for 200 ms, and then cuts off the supply to the coil.The timing circuit can be simple, just to time 200ms and give the cut-off signal.However, the timing circuit MUST REMAIN ‘ARMED’ AS LONG AS THE CLOSING COMMAND PERSISTS,so that it satisfies the anti-pumping requirement. When the command is removed, the timing circuit can re-set, so that it is ready for the next closure Design guide: Shunt tripCoil is intrinsically DC operated.If customer applies AC or DC, it will go through a rectifier bridge (can be SCR bridge), so that the coil only sees DC.The coil can be one, but may have to be double, with enough amp-turns to operate the plunger, and keep it held in Tripped condition.The electronics may need to be a little more complex than that of the CC, feeding the coil high AT during pickup, reducing it to the adequate holding AT, keeping the coil within acceptable temperature limits on cyclic duty and long term tests.

Design guide: Undervoltage releaseCoil is intrinsically DC operated. If customer applies AC or DC, it will go through a rectifier bridge (can be SCR bridge), so that the coil only sees DC.The coil has to be double, with enough amp-turns to operate the plunger, and keep it held in energised condition.The electronics will have to be the most complex of the three coils. It will have to feed enough AT to make the plunger pickup against a force of at least 10 N , reducing it to the adequate holding AT to keep it held against at least 16 N, keeping the coil within acceptable temperature limits on long term tests.Capacitor in a time delayed UV circuit should maintain enough AT during the time delay period to ‘hold’ the plunger in attracted position

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Coils for ACB

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Electronic circuit has  three  sections                      1 Obtaining power supply for the Electronic circuit                   2 Measuring and comparing the voltage based on that taking decision whether to activate driving circuit or not and  if so for how much time                   3 Driving circuit using MOSFETs which receive command from measuring and comparator ckt.In addition to this since the circuit has to withstand High impulse voltages there is a  varistor in the circuit  which limits the input voltage and protects the MOSFETsAc voltage is rectified and converted to DC.For obtaining  correct power supply zeners are used  which limit the voltages applied to electronic circuit including for reference and ICs.Resistance divider brings down the voltage to an appropriate level and feeds the same to the comparator. This voltage reaches the threshold at the set point of pick up and forces comparator to change its output .A pulse of the required time is generated by ‘RC’ network  and  is applied to MOSFET, which turns on  and operates the coil. On the second MOSFET a hold coil is connected and this MOSFET also turns on however it doesn’t turn off. As a result plunger remains operated even if pick up coil MOSFET turns off. Second MOSFET turns off  only when the voltage drops below the set limit.In case of closing coil there need be only one MOSFET, but for standardisation, we use the same PCB.There are jumpers to select type of the coil (CC or UV  or Shunt)  and voltage of the coil.The basic principle of  working for 110 V 220 V and 415 V is same. Except that the varistor rating changes … up to 220 V coils we use 275V varistor and for 415 V coils we use 550 V varistor

Design – continued ..The electronic system

Mosfet for pickup coil

Mosfet for hold coil

Pickup coil

Hold coil

Jumpers for selection of voltage

Jumpers for selection of type of coil

Capacitor used for antipumping function

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Coils for ACB

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Spec limits

IEC 60947 / IS 13947

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Coils for ACB

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New Spec limits for Shunt Releases

IEC 60947

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Coils for ACB

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Spec limits continued…

IEC 60947 / IS 13947

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Coils for ACB

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What options are there for a “Fallback (contingency) plan” ?

1. Interchange Pickup and Holding winding windows !a) Done in 2005b) Trade offs ,,, if Pickup goes better, hold goes worse and vice versa .. Dead end

2. Wind one winding OVER another !a) Done quite normally in Transformers and our own F Range contactorsb) + point is that we get a little more winding areac) - point is the need to insulate with tape the two windingsSeems to give some benefit.. Will use after the present design stabilises