Motor protection

Overload relay with reclosing lockout

They should always be used where

continuous contact devices (two-wire

control) are concerned (e.g. pressure and

position switches), to prevent automatic

restarting. The reset button can be fitted as

an external feature in order to make it

accessible to all personnel. Overload

relays for example are always supplied

with manual reset. but can be converted to

automatic reset by the user.

Overload relays without reclosing

lockout

They can be used only with pulsed contact

devices (three-wire control) such as

pushbuttons etc., because on these, the

cooling of the bimetal strips cannot lead to

automatic reconnection.

Special circuitry

Special circuitry such as is found in

star-delta switches, individually

compensated motors, current

transformer-operated overload relays etc.

may require that the relay settings deviates

from the motor rated operational current.

Frequently recurring operating cycles

It makes motor protection difficult. The

relay should be set to higher than rated

motor current in view of its shorter time

constant. Motors which are rated for a high

operating frequency will stand this setting

to a certain degree. Although this will not

ensure complete protection against

overload, it will nevertheless provide

adequate protection against non-starting.

Back-up fuses and instantaneous

releases

They are needed to protect not only the

motor, but also the relay, against the

effects of short-circuits. Their maximum

rating is shown clearly on every relay and

must be adhered to without fail. Higher

ratings – chosen for instance according to

the cable cross-section – would lead to the

destruction of the motor and relay.

The following important questions and

answers give a further guide to the

behaviour of an installation with motor

protection.

To what current must the overload relay

properly be set?

To the rated motor current – no higher, no

lower. A relay set to too low a figure will

prevent the full utilization of the motor; set

too high, it will not guarantee full overload

protection. If a correctly set relay trips too

frequently, then either the load on the

motor should be reduced or the motor

should be exchanged for a larger one.

When is it right for the overload relay to

trip?

Only when the current consumption of the

motor increases due to mechanical

overloading of the motor, undervoltage or

phase failure when the motor is under full

load or thereabout, or when the motor fails

to start due to a stalled rotor.

When does the overload relay fail to trip

in good time although the motor is

endangered?

With changes in the motor which do not

cause an increase in current consumption:

Effects of humidity, reduced cooling due to

a reduction in speed or motor dirt,

temporary additional external heating of

the motor or bearing wear.

What causes destruction of the overload

relay?

Destruction will take place only in the

event of a short-circuit on the load side of

the relay when the back-up fuse is rated

too high. In most cases, this will also

endanger the contactor and motor.

Therefore, always adhere to the maximum

fuse rating specified on every relay.

3-pole overload relays should be so

connected in the case of single-phase and

DC motors so that all three poles of the

overload relay carry the current, whether

in 1-pole or 2-pole circuits.

An important characteristic feature of

overload relays conforming to IEC/EN

60947-4-1 are the tripping classes (CLASS

10 A, 10, 20, 30). They determine different

tripping characteristics for the various

starting conditions of motors (normal

starting to heavy starting duty).

EATON

Earthing System TN-C-S

Motor Control Diagrams

Motor starters

Star-delta starter

 

This is the most popular and commonly

used starting method for motor ratings

> 4 kW (400 V).

 

• Electronic motor starter (EMS) and soft

starter

These enable the soft and low-noise

starting of the motor. This eliminates

interference producing current peaks

and jerks during switching. The startup

and deceleration phase of the motor can

also be time-controlled depending on the

load.

 

• Frequency inverter

This enables time-controlled motor

starting, motor braking and operation

with infinitely variable motor speeds.

Depending on the application, different

types of frequency inverters are used:

– with the voltage/frequency control

(U/f) or vector control for

frequency-controlled motor operation,

– with vector control or servo control for

high speed accuracy and additional

torque adjustment.

Associated circuit diagrams

Direct on line starter

Direct-on-line starter

 

In the simplest case the motor is

connected directly with a contactor. The

combination of motor protection and

cable protection (fuse) is called a motor

starter (MSC = Motor Starter

Combination).

By applying the full mains voltage to the

motor windings, DOL starting may

produce large starting currents which

may result in troublesome voltage

changes. Direct-on-line starting

three-phase motors must not cause

interference voltage changes in the

public utility grid. This requirement is

generally fulfilled if the apparent power

of a three-phase asynchronous motor

does not exceed 5.2 kVA or its startup

current does not exceed 60 A.

With a mains voltage of 400 V and 8 times

the starting current, this corresponds to

a rated motor current of around 7.5 A and

thus a motor rating of 4 kW.

The motor rating denotes the mechanical

output of the motor at the shaft.

CB Number of poles

Standards

CE

The CE conformity marking shall indicate conformity to all the obligations imposed

on the manufacturer, as regards his products, by virtue of the European

Community directives providing for the affixing of the CE marking.

 

When the CE marking is affixed on a product, it represents a declaration of the

manufacturer or of his authorized representative that the product in question

conforms to all the applicable provisions including the conformity assessment

procedures. This prevents the Member States from limiting the marketing and

putting into service of products bearing the CE marking, unless this measure

is justified by the proved non-conformity of the product.

Flow diagram for the conformity assessment procedures established by the Directive

2006/95/CE on electrical equipment designed for use within particular voltage range:

Manufacturer

Technical file

The manufacturer

draw up the technical

documentation

covering the design,

manufacture and

operation of the

product

EC declaration of

conformity

The manufacturer

guarantees and declares

that his products are in

conformity to the technical

documentation and to the

directive requirements

 

Naval type approval

The environmental conditions which characterize the use of circuit breakers for

on-board installations can be different from the service conditions in standard

industrial environments; as a matter of fact, marine applications can require

installation under particular conditions, such as:

- environments characterized by high temperature and humidity, including saltmist

atmosphere (damp-heat, salt-mist environment);

- on board environments (engine room) where the apparatus operate in the

presence of vibrations characterized by considerable amplitude and duration.

In order to ensure the proper function in such environments, the shipping registers

require that the apparatus has to be tested according to specific type

approval tests, the most significant of which are vibration, dynamic inclination,

humidity and dry-heat tests.

 

 

Standards

“Low Voltage” Directive 2006/95/CE

The Low Voltage Directive refers to any electrical equipment designed for use

at a rated voltage from 50 to 1000 V for alternating current and from 75 to

1500 V for direct current.

In particular, it is applicable to any apparatus used for production, conversion,

transmission, distribution and use of electrical power, such as machines,

transformers, devices, measuring instruments, protection devices and wiring

materials.

The following categories are outside the scope of this Directive:

• electrical equipment for use in an explosive atmosphere;

• electrical equipment for radiology and medical purposes;

• electrical parts for goods and passenger lifts;

• electrical energy meters;

• plugs and socket outlets for domestic use;

• electric fence controllers;

• radio-electrical interference;

• specialized electrical equipment, for use on ships, aircraft or railways, which

complies with the safety provisions drawn up by international bodies in which

the Member States participate.

 

Directive EMC 2004/108/CE (“Electromagnetic Compatibility”)

The Directive on electromagnetic compatibility regards all the electrical and electronic

apparatus as well as systems and installations containing electrical and/

or electronic components. In particular, the apparatus covered by this Directive

are divided into the following categories according to their characteristics:

• domestic radio and TV receivers;

• industrial manufacturing equipment;

• mobile radio equipment;

• mobile radio and commercial radio telephone equipment;

• medical and scientific apparatus;

• information technology equipment (ITE);

• domestic appliances and household electronic equipment;

• aeronautical and marine radio apparatus;

• educational electronic equipment;

• telecommunications networks and apparatus;

• radio and television broadcast transmitters;

• lights and fluorescent lamps.

The apparatus shall be so constructed that:

a) the electromagnetic disturbance it generates does not exceed a level allowing

radio and telecommunications equipment and other apparatus to operate

as intended;

b) the apparatus has an adequate level of intrinsic immunity to electromagnetic

disturbance to enable it to operate as intended.

An apparatus is declared in conformity to the provisions at points a) and b) when

the apparatus complies with the harmonized standards relevant to its product

family or, in case there aren’t any, with the general standards.

ABB MCC

Control Circuits

Control Circuits

Control  Control components are used in a wide variety of applications with varying degrees of complexity. One example of a simple control circuit is a circuit that turns a light on and off. In this circuit, the control component is often a single-pole switch.

 

 

Control circuits used in commercial and industrial applications tend to be more complex than this simple circuit and employ a broader variety of components. However, the function of these circuits is often the same, to turn something on and off. In some cases, manual control is used. More often, automatic control circuits or circuits that combine manual and automatic control are used.

 

 

Electrical Panel

Pollution Degree

The level of pollution in the environment in which the Assembly is intended to be

installed. Four categories are defined in the Standard as follows:

 

Pollution degree 1 : No pollution or only dry, non-conductive pollution occurs.

Pollution degree 2 : Normally, only non-conductive pollution occurs. Occasionally, however, a temporary

                             conductivity caused by condensation may be expected.

Pollution degree 3 : Conductive pollution occurs, or dry, non-conductive pollution occurs which becomes

                             conductive due to condensation.

Pollution degree 4 : The pollution generates persistent conductivity caused, for instance, by conductive dust or by

                             rain or snow.

 

Unless advised otherwise, the Standard and the manufacturer will assume

pollution degree 3 is applicable for industrial applications.

ROUTINE TESTS

These tests have a totally different function to Type Tests, BS EN 60439-1, states:

 

‘Routine tests are intended to detect faults in materials and workmanship. They are carried

out on every ASSEMBLY after its assembly or on each transport unit. Another routine test

at the place of installation is not required.’

 

Hence, Routine Tests on Assemblies are normally undertaken at the

manufacturer’s premises, and are:

• part of the quality control activity. They are intended to ensure materials and

workmanship included in every assembly produced meet the standards required

by the design.

• carried out on every assembly or transportable unit to be put into service. It is

recognized that it is unnecessary, with modern modular designs, to fully couple

assemblies for routine test, if they are subsequently to be shipped in several

sections.

• of a non-destructive nature having minimal effect on the service life of the

equipment.

• not intended to duplicate routine tests, previously carried out on components as

part of their manufacturing process.

• not intended to be repeated on site. This does not remove the onus of the

installer to ensure the assembly’s correct installation and obligation to test under

BS 7671. Before tests under BS 7671, or other testing is undertaken, the effects

of these tests on voltage sensitive components should be established.

 

(BEAMA Installation)