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)

PARTIALLY TYPE TESTED ASSEMBLY (PTTA)

IEC 60439-1, defines a PTTA as:

‘A low-voltage switchgear and controlgear assembly, containing both type-tested and nontype-

tested arrangements provided the latter are derived (e.g. by calculation) from type tested

arrangements which have complied with the relevant tests’.

 

This means:

• The assembly will be derived from a Type Tested Assembly.

• Deviations from the tested configuration are only permitted provided they can

be verified by calculation or equivalent methods. Such methods have their

limitations which must be fully understood and, where appropriate, allowed for

through safety factors in the analysis.

• As a means of demonstrating design compliance with the Standard,

manufacturers must have available Type Test documentation for the original

design and any calculations relating to modified elements.

• The Assembly will consist, as far as practical, of a series of standard elements

configured to suit a particular application. Customisation should be restricted to

situations where it cannot be avoided, e.g. facilities for terminating over size

cables, use of an alternative tested component, etc.

• All components and devices will be fully Type Tested to their respective product

standards. Documentation will be available for examination.

• Combinations of Type Tested components and devices installed in an otherwise

untested Assembly are not covered by this definition and the Standard.

 

(BEAMA Installation)

TYPE TESTED ASSEMBLY (TTA)

IEC 60439-1, defines a TTA as:

 

‘A low-voltage switchgear and controlgear assembly conforming to an established type or

system without deviations likely to significantly influence the performance, from the typical

ASSEMBLY verified to be in accordance with this standard.’

 

This means:

• The generic design of the Assembly including all the various elements used in its

construction have completed the Type Tests detailed in the Standard.

• Deviations from the tested configuration are permitted, but they will be very

minor and not ‘likely to significantly influence the performance’ e.g. a functional unit

may have been short circuit tested in the top of the Assembly and in service be

located lower down.

• Design verification must be via stringent testing, and does not rely on subjective

assessments, calculations, safety margins and engineering judgements.

• The Assembly will consist of a series of standardized elements including

interconnections, all of which have previously been proven by tests in the Type

Tested Assembly(s), but may be configured differently to suit the application.

• Assemblies may be built by licensed assemblers under strict controls.

 

(BEAMA Installation)

Current ratings

Rated current (In)

 

value of current, declared by the ASSEMBLY manufacturer taking into consideration the ratings

of the components, their disposition and application, which can be carried without the

temperature-rise of various parts of the ASSEMBLY exceeding specified limits under specified

conditions

 

Rated peak withstand current (Ipk)

value of peak short-circuit current, declared by the ASSEMBLY manufacturer, that can be

withstood under specified conditions

 

Rated short-time withstand current (Icw)

r.m.s value of short-time current, declared by the ASSEMBLY manufacturer, that can be carried

without damage under specified conditions, defined in terms of a current and time

 

Rated conditional short-circuit current (Icc)

value of prospective short-circuit current, declared by the ASSEMBLY manufacturer, that can be

withstood for the total operating time (clearing time) of the short-circuit protective device

(SCPD) under specified conditions

Voltage ratings

Rated voltage (Un) (of the ASSEMBLY)

The ASSEMBLY manufacturer shall state the rated voltage(s) necessary for correct functioning

of the ASSEMBLY.

 

Rated operational voltage (Ue) (of a circuit of an ASSEMBLY)

 

If different from the rated voltage of the ASSEMBLY, the ASSEMBLY manufacturer shall state the

appropriate rated operational voltage of the circuit.

The maximum rated operational voltage of any circuit of the ASSEMBLY shall not exceed its

rated insulation voltage.

 

Rated insulation voltage (Ui) (of a circuit of an ASSEMBLY)

 

The rated insulation voltage of a circuit of an ASSEMBLY is the voltage value to which dielectric

test voltages and creepage distances are referred.

The rated insulation voltage of a circuit shall be equal or higher than the values stated for Un

and for Ue for the same circuit.

NOTE For single-phase circuits derived from IT systems (see IEC 60364-5-52), the rated insulation voltage

should be at least equal to the voltage between phases of the supply.

 

Rated impulse withstand voltage (Uimp) (of the ASSEMBLY)

 

The rated impulse withstand voltage shall be equal to or higher than the values stated for the

transient overvoltage’s occurring in the system(s) to which the circuit is designed to be

connected.

IEC 61439 series

 

Electrical checks

Functional tests consist in checking the correct functioning

of all the circuits (electrical and electromechanical)

by simulating, as far as possible, the different service

conditions of the assembly.

For example, tests on current and voltage circuits can

be carried out by supplying the secondary circuits of

the CTs and VTs, without disconnecting the CTs from

the circuit.

Electrical checks may include the verification of the proper

operation of circuits and equipment, in particular:

- control, signaling, alarm, trip and reclosing circuits;

- lighting and heating circuits, if present;

- protection and measuring circuits (overcurrent, overvoltage,

earth, residual current trip units, contactors,

ammeters, voltmeters, etc.);

- terminals and contacts available in the terminal box;

- insulation control devices (also creepage distances

and clearances must be verified at level of connections

and adaptations carried out at workshop).

To carry out these checks, in addition to the normal mechanical

tools used for assembling, also some electrical

tools are necessary. A periodical calibration is necessary

to obtain reliable results.

The tools generally used are:

- a tester or multimeter;

- a test bench (AC and DC) to supply the assembly during

the test of the operation under voltage;

- a torque wrench (to check that the correct tightening

torques have been applied to the connections) and

other tools.

Mechanical checks

They shall be carried out complying with the relevant documents,

making reference to the following specifications:

- correct assembling of the equipment (connections

and, on a random basis, proper tightening of the connections);

- positioning and tightening of nuts and bolts;

- mechanical locks and controls (rack-in locking devices,

mechanical interlocks, key interlocks and

manual operating mechanisms for the removal of

circuit-breakers and switch-disconnectors by using

the operating levers and accessories provided with

the assembly);

- closing and possible blocks of the doors and adhesion

of the dust-proof seals to the assembly structure.

Further checks during testing

Visual inspections

They are carried out visually taking into account:

a) compliance of the assembly with diagrams, designations,

drawings and type of enclosures, number and

characteristics of equipment, cross-sectional area of

conductors and presence of identification marks on

cables and devices (initialing, inscriptions on plates,

etc.);

b) presence of components which allow the degree of

protection (roofs, seals) and the absence of faults on

the enclosure (cuts, perforations which might jeopardize

the degree of protection) to be guaranteed;

c) compliance with the specific prescriptions, if required

in the assembling list, such as:

- coating or treatment of busbars (resin coating, silver

plating, etc.);

- type of cable (fireproof, ecological, etc.);

- completion spare parts;

- painting check (color, thickness, etc.).