Coils overview rev2

download

of 15

  • date post

    24-Nov-2014
  • Category

    Documents

  • view

    112
  • download

    4

Embed Size (px)

Transcript of Coils overview rev2

Coils for ACB

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

*

C&S Proprietary, Duplication Permission Required

1

Coils for ACBMECHANICAL PARTYoke Snap-fit spring Coil 1 Pole piece 1 Pole piece 2 St.steel plunger St. steel Return Spring Armature (moving core) Coil 2

Electronics

Non-magnetic spacer

C&S Proprietary, Duplication Permission Required

2

Coils for ACBTRAVEL Constructional difference between CC/ST and UV

Travel in all coils is 9 mm

C&S Proprietary, Duplication Permission Required

3

Coils for ACBELECTRICAL PART COILWhy two coils ?32 6.5 20

For pickup, we require a high AT For holding, we require much less Why not for Closing coil ?

Dm

15

It does not need to hold on. It should operate once and come back. About 200 ms ON Why ? Length of mean turn =

T * (15 + 6) (allowing 0.5mm for tape) = T * 21 = 65.97 mmLm * No of turns = Total length of wire

Electrical anti-pumping

C&S Proprietary, Duplication Permission Required

4

Coils for ACBDesign

C&S Proprietary, Duplication Permission Required

5

Coils for ACBDesign continued ..

C&S Proprietary, Duplication Permission Required

6

Coils for ACBDesign 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 Having established the AT required for pickup and hold a) Try various gauges of wire to see which ones work.* b) Wind the coils c) Test them alone d) Then with electronics e) Then with ACB f) Then for cyclic performance g) Then for continuous heat-run * see the slide after the next one for explanation Simple isnt it ?7

2.

C&S Proprietary, Duplication Permission Required

Coils for ACBNot 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 ?C&S Proprietary, Duplication Permission Required

8

Coils for ACB 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 odesign is based on 1.68 Q;cm resistivity of copper which is true for annealed copper @ 20 C. Due to work-hardening, and some other reasons, it can go up to 1.73 Q;cm When coil resistance is measured, the ambient temperature must be noted, and a o correction factor applied. This factor is 0.00393 / C IEC specifies 8% tolerance on resistance per meter of Copper wire Coil resistance must be measured using the resistance method. A calculator is available.C&S Proprietary, Duplication Permission Required

Design continued ..

E

9

Coils for ACBDesign continued ..Design guide: Closing coil Coil 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 trip Coil 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 release Coil 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

C&S Proprietary, Duplication Permission Required

10

Coils for ACBDesign continued ..Mosfet for pickup coil Mosfet for hold coil Pickup coil Hold coil

The electronic systemElectronic 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 MOSFETs Ac 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 doesnt 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

Jumpers for selection of voltage Jumpers for selection of type of coil

Capacitor used for antipumping functionC&S Proprietary, Duplication Permission Required

11

Coils for ACBSpec limits IEC 60947 / IS 13947

C&S Proprietary, Duplication Permission Required

12

Coils for ACBNew Spec limits for Shunt Releases IEC 60947

C&S Proprietary, Duplication Permission Required

13

Coils for ACBSpec limits continued IEC 60947 / IS 13947

C&S Proprietary, Duplication Permission Required

14

Coils for ACBWhat options are there for a Fallback (contingency) plan ? 1. Interchange Pickup and Holding winding windows ! a) Done in 2005 b) Trade offs ,,, if Pickup goes better, hold goes worse and vice versa .. Dead end Wind one winding OVER another ! a) Done quite normally in Transformers and our own F Range contactors b) + point is that we get a little more winding area c) - point is the need to insulate with tape the two windings Seems to give some benefit.. Will use after the present design stabilises

2.

C&S Proprietary, Duplication Permission Required

15