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INDEX

MOTOR RUN CAPACITORS

1. MKP Capacitors for Motor Run Applications

2.S ingle-phase induction motors

3.O peration of three-phase Motors in single-phase supply

4.H ow to calculate the single-phase motor start capacitor

5.S election of capacitance on motor capacitors Facts and Formulas

6.T echnical Specifications

7. Table for Single Phase Motor Run Capacitor

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2

2

3

4

5

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MKP CAPACITORS FOR MOTOR RUN APPLICATIONMotor capacitors are operation capacitors for single-phase induction motors with auxiliary winding and three-phase motor in Steinmetz circuits. Motor capacitors are permanently connected to the windings

of the motor, so that both motor and capacitor have the same mode of operation.Motor capacitors are self-healing capacitors, i.e. a weak point in the dielectric would become ineffective by itself since the metal coating evaporates at the weak point. Capacitors used in this way should be carefully selected as far as voltage rating is concerned, and special attention should be paid to the method of operation (continuous or intermittent). The voltage developed across the capacitor terminals is, usually, higher than the supply voltage. Motor capacitors are utilized mainly in the following fields: Household and domestic appliances Office machines Heating and ventilation techniques Garden and recreational equipment.Single-phase induction motorsThe single-phase motors has two windings. The main winding is supplied directly from the mains, whereas the auxiliary winding supply is provided by the capacitance of the series-connected capacitor /fig.1/. The capacitance is selected so that the auxiliary winding is able to take up the capacitor current continuously. No switching devices are necessary for the auxiliary winding circuit, so that in respect of operating reliability the single phase capacitor start and run motor is in no way inferior to a three-phase cage rotor motor. The motor is superior to a single-phase motor in Steinmetz connection in so far as it can be adapted to a considerable degree to the drive requirements by an appropriate winding layout. Also the capacitance of the capacitor used here is smaller in relation to an identical motor out-put.Single-phase capacitor start and run motors are suitable only for driving machines which do not require the full rated output of the motor for starting. The performance requirements for the capacitor depend on the output power or torque and the design of the motor. If the capacitor is to operate in conjunction with a 220V.50 Hz single phase motor whose main and auxiliary windings have the same number of turns, then a capacitance of approximately 30 to 50 mF per kW of the rated motor output power should be used.Operation of three-phase Motors in single-phase supplyInduction motors with a three-phase stator winding can either be driven from a three-phase supply or from a single-phase supply when suitably connected with a capacitor (The circuit Fig. 2a and fig. 2b). A three-phase induction motor with its stator connected in star for a 380V three-phase supply has 220V as phase voltage. The motor can therefore also run on a 220V three phase supply when delta connected. If the motor is designed for 125/220V then its phase voltage is only 125V and the motor must be connected in star for a three-phase supply of 220V.The circuit gives similar characteristics to three phase operation but with a single-phase supply. The motor runs as a three-phase machine, if the capacitor voltage causes a symmetrical voltage star at the rotor windings as with a three-phase supply. A symmetrical voltage distribution can however only be obtained with a certain capacitor at a certain load. For all other loads an asymmetrical voltage star is formed at the rotor, so that the motor can no longer operate under optimum conditions. The starting torque is reduced and the heat generation in the motor can become higher at no load than at full load. Experience has shown that with a voltage supply of 220V, 50 Hz, a capacitance of 70 mF/kW of motor power is necessary in order to give a starting torque of 30% of rated torque and in operation about 80% of the rated three-phase power.In order to obtain a higher starting torque, a starting capacitor with about double the capacitance must be connected in parallel. This must be switched off during run up to avoid overloading the motor. The direction of rotation can be reversed by connecting the capacitor to the other supply connection. The voltage across the capacitor terminals in the “Steinmetz” circuits is, at the rated power of the motor, about the value of the supply voltage, and under no load about 15% higher. If the “open star circuit” should be used for a special application please state this when ordering in order that the correct capacitor can be supplied. This circuit can be used when 125/220V three-phase motors are tooperated from a 220V single-phase supply.

2

Auxiliary winding motor with continuous operation capacitor a/ Star connection b/ Delta connection Fig ( 1 ) Fig (2 )

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How to calculate the single-phase motor start capacitorHow to calculate the single-phase motor start capacitorGenerally do not have to calculate the start capacitor is only played to a phase-shifting effect, and the starting coil with the coil emfphase shift Difference between each of the electrical angle of 180 ° to produce a rotating magnetic field after the motor starts to cut off the start-up coil and capacitor, so the capacitance range of applications Wide general 550W-2200W motor with 450V200μf can start.The rotation of AC motors rely on rotating magnetic field generated by the current. Three-phase motor flows through the phase difference of 120 degrees of phase current, can produce a rotating magnetic Field. Single-phase motor flow through the single-phase current cannot produce a rotating magnetic field, the need to take some method to make it a rotating magnetic field, with capacitance is Method, is one of the most common method .The capacitor is used to phase separation, the current near 90 ° phase difference to produce a rotating magnetic field . Three-phase electricity, each Current between the two-phase itself phase, without phase separation. The capacitor induction motor has two windings, a start winding and run winding. The two windings in space, a difference of 90 degrees. Start winding thread A larger capacity capacitor, when the run winding and start winding through the individual AC capacitor role in the start winding current In time than the running winding current ahead of the 90-degree angle before reaching the maximum. The formation of two identical pulse magnetic field, so that fixed in time and space The air gap between the child and the rotor of a rotating magnetic field, the role of the rotating magnetic field, the induced current in the motor rotor, the current and spin Turn the magnetic field interaction of the electromagnetic torque, the motor spin up. Single-phase motor capacitor formula: GC = 1950I/Ucos� (micro-method) in which:?I: motor current, U: single-phase supply voltage, the cos �: power factor, to take 0.75,1950: Constant Calculate the single-phase motor capacitor , starting capacitor capacitance of work 1-4 times.

-Run configura�on comprises two windings (start winding W1), (Run windings W2) , centrifugal switch(SW1) and

two -Start Capacitor C1 and Run capacitor C2

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Selection of capacitance on motor capacitors Facts and Formulas

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Technical Specifications

250 - 400 Vac

50 - 60 Hz.

+-10%

-25 - +85

<<0,002 ( 50 Hz )

2Un for 2 sec.

1.1 Un

1.3 In

Flame Reterdant

wire Tag 6.3 mm

Polyurethane

Non-PCB, No leakage

Materials

3000h ( C ) - 10000h( B )

Nominal Voltage ( Un )

Nominal Frequency ( Fn )

Tolerance

Working temperature

Dissipation Factor

Voltage test between terminals

Max. Permissible over voltage

Max. Permissible over current

Case

External Terminal

Filling resin

Compatibilty with

Environment

Life expectancy

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KRK-2-250-M

KRK-2.5-250-M

KRK-3-250-M

KRK-3,5-250-M

KRK-4-250-M

KRK-4,5-250-M

KRK-5-250-M

KRK-6-250-M

KRK-7-250-M

KRK-7,5-250-M

KRK-8-250-M

KRK-9-250-M

KRK-10-250-M

KRK-12-250-M

KRK-12,5-250-M

KRK-15-250-M

KRK-16-250-M

KRK-18-250-M

KRK-20-250-M

KRK-25-250-M

KRK-30-250-M

KRK-35-250-M

KRK-40-250-M

KRK-45-250-M

KRK-50-250-M

KRK-60-250-M

KRK-65-250-M

KRK-80-250-M

KRK-2-400-M

KRK-2,5-400-M

KRK-3-400-M

KRK-3,5-400-M

KRK-4-400-M

KRK-4,5-400-M

KRK-5-400-M

KRK-6-400-M

KRK-7-400-M

KRK-7,5-400-M

KRK-8-400-M

KRK-9-400-M

KRK-10-400-M

KRK-12-400-M

KRK-12,5-400-M

KRK-15-400-M

KRK-16-400-M

KRK-18-400-M

KRK-20-400-M

KRK-25-400-M

KRK-30-400-M

KRK-35-400-M

KRK-40-400-M

KRK-45-400-M

KRK-50-400-M

KRK-60-400-M

KRK-65-400-M

KRK-80-400-M

2

2,5

3

3,5

4

4,5

5

6

7

7,5

8

9

10

12

12,5

15

16

18

20

25

30

35

40

45

50

60

65

80

25x65

25x65

25x65

25x65

25x65

25x65

25x65

25x65

32x65

32x65

32x65

32x65

32x65

34,5x65

34,5x65

36x65

36x65

40x65

40x65

46x65

46x65

52x65

52x65

63x65

63x65

63x65

71x65

71x65

128

128

128

128

128

128

128

128

84

84

84

84

84

65

65

65

65

50

50

32

32

28

28

18

18

18

16

15

250V 400VCAP

µfDxH (mm)

BOX Quantity

SINGLE PHASE MOTOR RUN CAPACITOR

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TABLE (1)