Definitions and Terminology
1. All-or-nothing relay
output of measuring transformers, expressed in VA, is always at
rated current or voltage and it is important, in assessing the
burden imposed by a relay, to ensure that the value of burden at
rated current is used.
18. Effective range
The range of values of the
characteristic quantity or quantities, or of the energizing
quantities to which the relay will respond and satisfy the
requirements concerning it, in particular those concerning
19. Effective setting
The 'setting' of a protective system
including the effects of current transformers. The effective setting
can be expressed in terms of primary current or secondary current
from the current transformers and is so designated as appropriate.
20. Electrical relay
A device designed to produce sudden predetermined changes in one or more electrical circuits after the appearance of certain conditions in the electrical circuit or circuits controlling it.
NOTE: The term
'relay' includes all the ancillary equipment calibrated with the
21. Energizing quantity.
quantity, either current or voltage, which alone or in combination
with other energizing quantities, must be applied to the relay to
cause it to function.
22. Independent time delay relay.
A time delay
relay in which the time delay is independent of the energizing
21. Instantaneous relay.
A relay which operates and resets with no intentional time delay.
NOTE: All relays require some time to operate; it is possible, within the above definition, to discuss the operating time characteristics of an instantaneous relay.
A dependent time delay relay having an operating time which is an inverse function of the electrical characteristic quantity.
A relay in which the time delay varies inversely with the characteristic quantity up to a certain value, after which the time delay becomes substantially independent.
That sinusoidal e.m.f. applied to the secondary terminals of a current transformer, which, when increased by 10 %, causes the exciting current to increase by 50%.
The protective system which is normally expected to operate in response to a fault in the protected zone.
26. Measuring relay.
A relay intended to operate with a specified accuracy at one or more values of its characteristic quantity.
A relay which switches in response to a specific number of applied impulses.
With a relay de-energized and in its initial condition, the time which elapses between the application of a characteristic quantity and the instant when the relay operates.
The curve depicting the relationship between different values of the characteristic quantity applied to a relay and the corresponding values of operating time.
The limiting value of the characteristic quantity at which the relay actually operates.
The extent to which the condition that leads to final operation is advanced after the removal of the energizing quantity, expressed as time at the rate of progress of the said condition appropriate to the value of the energizing quantity that was initially applied.
A relay is said to 'pick-up' when it changes from the un-energized position to the energized position.
A means of interconnection between relaying points for the purpose of protection.
The portion of a power system protected by a given protective system or a part of that protective system.
The apparatus, including protective relays, trans-formers and ancillary equipment, for use in a protective system.
A relay designed to initiate disconnection of a part of an electrical installation or to operate a warning signal, in the case of a fault or other abnormal condition in the installation. A protective relay may include more than one unit electrical relay and accessories.
The coordinated arrangements for the protection of one or more elements of a power system.
A protective scheme may comprise several protective systems.
A combination of protective gear designed to secure, under predetermined conditions, usually abnormal, the disconnection of an element of a power system, or to give an alarm signal, or both.
The nominal value of an energizing quantity which appears in the designation of a relay. The nominal value usually corresponds to the CT and VT secondary ratings.
The limiting value of the characteristic quantity at which the relay returns to its initial position.
The algebraic sum, in a multi-phase system, of all the line currents.
The algebraic sum, in a multi-phase system, of all the line-to-earth voltages.
The limiting value of a 'characteristic' or 'energizing' quantity at which the relay is designed to operate under specified conditions.
Such values are usually marked on the relay and may be expressed as direct values, percentages of rated values, or multiples.
The quality whereby a protective system remains inoperative under all conditions other than those for which it is specifically designed to operate.
value of the symmetrical component of the through fault current up
to which the protective system remains stable.
46. Starting relay.
A unit relay which responds to abnormal conditions and initiates the operation of other elements of the protective system.
The ratio of the power system source impedance to the impedance of the protected zone.
The current flowing through a protected zone to a fault beyond that zone.
49. Time delay.
A delay intentionally introduced into the operation of a relay system.
A relay having an intentional delaying device.
A single relay which can be used alone or in combinations with others.
A protection system which is designed to operate only for abnormal conditions within a clearly defined zone of the power system.
system which has no clearly defined zone of operation and which
achieves selective operation only by time grading.
For the purpose of this International Standard, the following definitions, some of them based on IEC 60050(191), IEC 60050(212) and
IEC 60050(604) apply:
An unplanned occurrence or defect in an item which may result in one or more failures of the item itself or of other associated equipment
NOTE - In electrical equipment, a fault may or may not result in damage to the insulation and failure of the equipment.
2- Non-damage fault
A fault which does not involve repair or replacement action at the point of the fault
NOTE - Typical examples are self-extinguishing arcs in switching equipment or general overheating without paper carbonization.
3- Damage fault
A fault which involves repair or replacement action at the point of the fault
[IEC 604-02-08, modified]
An event related to an internal fault which temporarily or permanently disturbs the normal operation of an equipment [IEV 604-02-03, modified]
NOTE - Typical examples are gas alarms, equipment tripping or equipment leakage.
The termination of the ability of an item to perform a required function [IEC 191-04-01]
NOTE - In the electrical equipment, failure will result from a damage fault or incident necessitating outage, repair or replacement of the equipment, such as internal breakdown, rupture of tank, fire or explosion.
6- Electrical fault
a partial or disruptive discharge through the insulation.
7- Partial discharge
A discharge which only partially bridges the insulation between conductors. It may occur inside the insulation or adjacent to a conductor
[IEC 212-01-34, modified]
NOTE 1 - Corona is a form of partial discharge that occurs in gaseous media around conductors which are remote from solid or liquid insulation. This term is not to be used as a general term for all forms of partial discharges.
NOTE 2 - X-wax is a solid material which is formed from mineral insulating oil as a result of electrical discharges and which consists of polymerized fragments of the molecules of the original liquid
[IEV 212-07-24, modified].
Comparable products may be formed from other liquids under similar conditions.
NOTE 3 - Sparking of low energy, for example because of metals or floating potentials, is sometimes described as
Partial discharge but should rather be considered as a discharge of low energy.
8- Discharge (disruptive) .
The passage of an arc following the breakdown of the insulation
[IEC 604-03-38, modified]
NOTE 1 - Discharges are often described as arcing, breakdown or short circuits.
The more specific following terms are also used:
- spark over (discharge through the oil);
- puncture (discharge through the solid insulation);
- Flashover (discharge at the surface of the solid insulation);
- tracking (the progressive degradation of the surface of solid insulation
Discharges to form conducting or partially conducting paths);
- sparking discharges which, in the conventions of physics, are local
Dielectric breakdowns of high ionization density or small arcs.
NOTE 2 - Depending on the amount of energy contained in the discharge, it will be described as a discharge of low or high energy, based on the extent of damage observed on the equipment .
9- Thermal fault
Excessive temperature rise in the insulation
NOTE - Typical causes are
- Insufficient cooling,
- Excessive currents circulating in adjacent metal parts (as a result of bad
Contacts, eddy currents, stray losses or leakage flux),
- Excessive currents circulating through the insulation (as a result of high
Dielectric losses), leading to a thermal runaway,
- overheating of internal winding or bushing connection lead.
10- Typical values of gas concentrations.
gas concentrations normally found in the equipment in service which have no symptoms of failure, and which are over passed by only an arbitrary percentage of higher gas contents, for example 10 % .
NOTE 1 - Typical values will differ in different types of equipment and in different networks, depending on operating practices (load levels, climate, etc.).
NOTE 2 - Typical values, in many countries and by many users, are quoted as "normal values", but this term has not been used here to avoid possible misinterpretations.
LIST OF DEVICE NUMBERS
· 2 Time delay starting or closing relay.
· 3 Checking or interlocking relay
· 21 Distance relay
· 25 Synchronizing or synchronism check relay
· 27 Under voltage relay
· 30 Annunciator relay
· 32 Directional power relay
· 37 Undercurrent or under power relay
· 40 Field failure relay
· 46 Reverse phase or phase balance current relay
· 49 Machine or transformer thermal relay
· 50 Instantaneous over current or rate-of-rise relay
· 51 A.c. time over current relay
· 52 A.c. circuit breaker
· 52a Circuit breaker auxiliary switch—normally open
· 52b Circuit breaker auxiliary switch—normally closed
· 55 Power factor relay
· 56 Field_application relay
· 59 Over voltage relay
· 60 Voltage or current balance relay
· 64 Earth fault protective relay
· 67 A.c. directional over current relay
· 68 Blocking relay
· 74 Alarm relay
· 76 D.c. over current relay
· 78 Phase angle measuring or out-of-step protective relay
· 79 A.c. reclosing relay
· 81 Frequency relay
· 83 Automatic selective control or transfer relay
· 85 Carrier or pilot wire receive relay
· 86 Locking-out relay
· 87 Differential protective relay
auxiliary tripping relay