Effect of the cable capacitance of Long Control Cables on the - Moeller

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Effect of the cable capacitance of Long Control Cables on the - Moeller

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ong>Effectong> ong>ofong> ong>theong> Cable Capacitance

ong>ofong> ong>Longong> ong>Controlong> ong>Cablesong> on

ong>theong> Actuation ong>ofong> Contactors

Technical Paper

Dipl.-Ing. Dirk Meyer


The problem ong>ofong> ong>cableong> ong>capacitanceong> with long control ong>cableong>s also ong>ofong>ten occurs in large-scale installations such as with crane systems in container

terminals.

The contactor is ong>theong> most important switching device in industrial and commercial applications. Its importance has

furong>theong>r increased due to ong>theong> influence ong>ofong> automation. This has given rise to some significant advancements in ong>theong>

development ong>ofong> contactors, ong>ofong> which ong>theong> user is ong>ofong>ten not aware. For example, ong>theong> power required for switching has

been considerably reduced in recent years due to ong>theong> use ong>ofong> integrated actuation electronics.

Despite ong>theong> many benefits made possible by ong>theong> reduced power consumption, such as

- Energy savings

- Use ong>ofong> smaller control transformers

- ong>Longong>er service life ong>ofong> control contacts

ong>theong> reduced power requirements must be particularly taken into account with applications involving long control ong>cableong>s.

Reliable contactor disconnection on actuation ong>ofong> ong>theong> command device also depends on ong>cableong> length, due to ong>theong> ong>cableong>

ong>capacitanceong> between ong>theong> command device and ong>theong> contactor coil.

2


1. Cable ong>capacitanceong>s

In certain circumstances, long control

ong>cableong>s in AC actuated control circuits

may prevent ong>theong> disconnection ong>ofong> contactors

due to ong>theong> ong>cableong> ong>capacitanceong> present.

Even if ong>theong> command contacts are open,

ong>theong> coil current can still flow due to ong>theong>

ong>cableong> ong>capacitanceong> so that ong>theong> contactor

remains in ong>theong> On position if sufficient

sealing current is present.

The effect ong>ofong> ong>cableong> ong>capacitanceong> depends

on ong>theong> design ong>ofong> ong>theong> control current circuit:

1.1 Capacitance ong>ofong> control ong>cableong>s

A guide value for control ong>cableong> ong>capacitanceong>s

between two conduc tors is

approx. 0.3µF per km for two-wire control,

and approx. 0.6µF per km between

three conductors for three-wire control.

The following equation should be used:

C L = 0.3 (µF/km) x l (km)

Two-wire control (1.3)

C L = 0.6 (µF/km) x l (km)

Three-wire control (1.4)

On disconnection, C L2 and C L3 are

switched in parallel (C L1 is bridged by

Q11). However, ong>theong> specific values

depend on ong>theong> ong>cableong> used and may ong>theong>refore

vary. If necessary, obtain ong>theong> ong>cableong>

ong>capacitanceong> from ong>theong> manufacturer.

When laying control ong>cableong>s togeong>theong>r with

oong>theong>r lines (e.g. in ong>theong> ong>cableong> duct), ong>theong>

ong>cableong> ong>capacitanceong> can no longer be calculated.

The capacitive currents must be

measured.

L1

N

L1

N

Q11

C L

C L

Two-wire control:

C L = 0.3 (µF/km) x l (km) (1.3)

C L

l

l

L1

N

I

0

Q11

L1

N

Q11

Q11

C L1

C L3

C L2

Three-wire control:

C L = 0.6 (µF/km) x l (km) (1.4)

Q11

No effect ong>ofong> ong>cableong> ong>capacitanceong> C L if ong>theong> command contact is located close to ong>theong> power supply.

There may be a slight ong>ofong>f-delay due to C L.

ong>Effectong> ong>ofong> ong>cableong> ong>capacitanceong> C L if ong>theong> command contact is located away from ong>theong> power supply.

The coil current continues to flow even when ong>theong> command contact is opened.

3


2. Limit ong>capacitanceong> ong>ofong> a contactor

The maximum ong>capacitanceong> at which ong>theong>

contactor stays switched on in ong>theong> new

condition despite ong>theong> ong>ofong>f command can

be calculated using ong>theong> equation below:

b PH ·106 1 + a o · U 2

C max = · [mF] (2.0)

C

with

UAB

a = = 0,4

UC b

I

= AB = 0,25...0,35

IC U AB = minimum drop-ong>ofong>f voltage in V

I AB = Sealing current with a mini mum

drop-ong>ofong>f voltage in A

P H = Rated sealing current ong>ofong> ong>theong> contactor

in VA

U C = Rated control supply voltage in V

At 50 Hz and a permissible rated control

supply voltage 110% times rated voltage

based on equation 2.0:

PH Cmax = 500 · [mF]

U 2

C

3. Determining ong>theong> maximum permissible

control ong>cableong> lengths

In order for a contactor to switch correctly,

C L must be less than C max.

If equations (1.3) and (1.4) are related to

equation (2.1), ong>theong> following values are

produced for 50 Hz networks:

Single einfache control Steuerleitungslänge ong>cableong> lengths in m

100000

1000

PH U 2

C

l zul = 1,7 · 10 6 · [m]

Two-wire control (3.0)

24V 50Hz 24V 50Hz

10

1 10

Sealing Halteleistung power in in VA VA

100

120V 60Hz

120V 60Hz

230V 50Hz

240V 60Hz

230V 50Hz

240V 60Hz

400V 50Hz

400V 50Hz

Dauerkontaktgabe

Two-wire control

Three-wire Impulskontaktgabe control

At 60 Hz ong>theong> values must be reduced by

20%. Permissible single control ong>cableong> length with a rated actuation voltage ong>ofong> 110% UC in relation to

ong>theong> contactor sealing power

PH U 2

C

l zul = 0,85 · 10 6 · [m]

Three-wire control (3.1)

l perm = maximum permissible control

ong>cableong> length in m.

With 60Hz networks ong>theong> values for (3.0)

and (3.1) must be reduced by 20%.

4


CONTACTOR

U C = 230 V

DILE(E)

DILM7...DILM15; DILA; DILMP20

DILM17...DILM38; DILMP32; DILMP45

DILM40...DILM72; DILMP63; DILMP80

DILM80; DILM95

DILM115...DILM170; DILMP125...DILMP200

DILM185...DILM250

DILM300...DILM570

DILM580...DILM1000

DILH1400

DILH2000; DILH2200; DILM1600

U C = 120 V

DILE(E)

DILM7...DILM15; DILA; DILMP20

DILM17...DILM38; DILMP32; DILMP45

DILM40...DILM72; DILMP63; DILMP80

DILM80; DILM95

DILM115...DILM170; DILMP125...DILMP200

DILM185...DILM250

DILM300...DILM570

DILM580...DILM1000

DILH1400

DILH2000; DILH2200; DILM1600

4. Measures to counteract excessive

ong>cableong> ong>capacitanceong>

Several solutions are possible if ong>theong> engineering

ong>ofong> an installation determines that

ong>theong> contactors will not drop out due to

excessive ong>cableong> ong>capacitanceong>:

Use ong>ofong> contactors with higher coil sealing

power

Use ong>ofong> DC operated contactors

Reduction ong>ofong> ong>theong> control supply voltage

(allow for voltage drop)

Laying ong>theong> supply ong>cableong> near ong>theong> command

contacts

An additional NC contact for two-wire

control and NO contact for three-wire

control are used to short ong>theong> coil.

An additional ong>cableong> is required for this.

This considerably increases ong>theong> break

times ong>ofong> ong>theong> contactors

Parallel switching ong>ofong> a resistance. The

resistance is calculated as follows:

1000

R = [O] CL in µF (4.1)

CL L1

N

I

0

Sealing

power

VA

4.6

4

8

16

26

3.5

4.3

4.3

7.5

7.5

15

4.6

4

8

16

26

3.5

4.3

4.3

7.5

7.5

15

Q11

Maximum permissible ong>cableong> length in m for

Two-wire

control

50Hz

148

129

257

514

836

112

138

138

241

241

482

543

472

944

1889

3069

413

508

508

885

885

1771

Three-wire

control

50Hz

74

64

129

257

418

56

69

69

121

121

241

272

236

472

944

1535

207

254

254

443

443

885

L1

N

Q11

Two-wire

control

60Hz

118

103

206

411

668

90

111

111

193

193

386

434

378

756

1511

2456

331

406

406

708

708

1417

Three-wire

control

60Hz

Maximum permissible single control ong>cableong> length for a rated control supply voltage ong>ofong> 230V and 120V and a maximum control supply voltage ong>ofong> 1.1

x UC for 50 Hz and 60 Hz mains frequency.

Two-wire control

Three-wire control

The power ong>ofong> ong>theong> resistance is:

U 2

C P = [W]

R

59

51

103

206

334

45

55

55

96

96

193

217

189

378

756

1228

165

203

203

354

354

708

(4.2)

It must be taken into account that ong>theong>

resistor increases ong>theong> total heat dissipation

ong>ofong> ong>theong> circuit.

5


Eaton Corporation

Eaton is a leading power

management company. Eaton

operates worldwide with products,

systems and services in ong>theong>

electrical, hydraulic, aerospace,

truck and automotive sectors.

Eatons Electrical Sector

Eatons Electrical Sector is ong>theong>

worldwide leader in products,

systems and services for energy

distribution, safe electricity supply

and automation in industrial,

residential and purpose-built

buildings, public facilities, energy

providers, commerce and OEMs.

Eaton Electrical Sector includes ong>theong>

brands Cutler-Hammer ® , Moeller ® ,

Micro Innovation, Powerware ® ,

Holec ® , MEM ® and Santak ® .

www.eaton.com

Addresses worldwide:

www.moeller.net/address

E-Mail: info-int@eaton.com

Internet: www.eaton.com/moellerproducts

www.eaton.com

Publisher:

Eaton Corporation

Electrical Sector – EMEA

Eaton Industries GmbH

Hein-Moeller-Str. 7–11

D-53115 Bonn

© 2005 by Eaton Industries GmbH

Subject to alterations

VER2100-949GB ip 11/10

Printed in Germany (11/10)

Article No.: 121410

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