Operate electrical switchgear in the electricity supply industry
Operate electrical switchgear in the electricity supply industry US 12387
Training and Assessment Resource Level 4 Credits 6
Electricity Supply Indu...
Switchgear medium 8 Oil filled switchgear 8 Air insulated switchgear 10 Vacuum switchgear 12 SF6 switchgear 13
3.0 Switchgear components 15 3.1 Operating mechanisms 15 3.2 Switchgear enclosures 27 3.3 Closing and release mechanisms 30 3.4 Interlocks 30 3.5 Grading capacitors 37 3.6 Anti-pumping mechanisms 37 3.7 Closing and trip coils 37 3.8 Trip circuit supervision 38 3.9 Slow closing mechanism 38 3.10 Communications 38 3.11 Auxiliary plant 38 3.12 Direct current (DC) systems 38 3.13 Earthing 39 3.14 Operating rods 39 3.15 Current and voltage transformer 39 4.0 4.1 4.2 4.3 4.4 4.5 4.6
Types of switchgear Circuit breakers Reclosers and sectionalisers Disconnectors Earth switches Point of wave switching Resource management act 1991 (RMA)
40 40 42 45 46 48 48
5.0 Switchgear numbering 49 5.1 High voltage switchgear numbering 49 5.2 Location or circuit identifier 49
TAR 12387 | Edition 1 2011
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5.3 5.4 5.5 5.6
Equipment code Unit number or unique identifier Equipment number 11kv indoor switchgear numbering
50 50 51 51
6.0 Operator responsibilities 6.1 Prior to operating switchgear 6.2 Safety tips when operating switchgear
52 52 53
Answers to activities
55
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TAR 12387 | Edition 1 2011
Introduction to Training Assessment Resource This Training Assessment Resource (TAR) contains the information that you require to complete the written assignment in the assessment pack for this unit standard. Purpose People who obtain credit for this unit standard are able to:
Demonstrate knowledge of electrical switchgear in common use in electricity supply systems.
Describe the operating principles of switchgear in common use in electricity supply systems.
Identify and communicate switchgear status.
Operate electrical switchgear under normal service conditions.
Operate electrical switchgear in response to unplanned events.
Report electrical switchgear operation.
Getting started on the ESITO Training & Assessment Resources Activity: A written or spoken exercise or assignment.
Keypoint: Important information to remember.
TAR 12387 | Edition 1 2011
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Glossary When I see this word
It means
Bellows
Flexible connection between two compartments, used to ensure that compartments remain sealed.
Cam
A cam is a rotating or sliding piece in a mechanical linkage used especially in transforming rotary motion into linear motion or vice-versa.
Crude
Rough.
Dielectric strength
Dielectric strength of an insulating material is the maximum electrical field strength the material can withstand before breaking down.
Fluctuations
Unpredictable movements.
Inrush Current
The large current that is drawn when a transformer is switched into the circuit.
Instantaneous
Occurring, arising, or functioning without any delay; happening within an imperceptibly brief period of time.
Ionization
The physical process of converting an atom or molecule into an ion by adding or removing charged particles such as electrons or other ions.
Phenomenon
A fact or occurrence that appears or is perceived.
Tolerance
The permissible limit or limits.
Velocity
Speed in a given direction.
Pneumatic
Energy stored in the form of air pressure.
Sacrificial
Something that is allowed to be damaged to prevent damage to another component.
Satellite
Remote/removed from the main unit.
Sprocket
A sprocket is a profiled wheel with teeth that meshes with a chain, track or other perforated or indented material. It is distinguished from a gear, in that sprockets are never meshed together directly, and differs from a pulley, in that sprockets have teeth and pulleys are smooth.
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TAR 12387 | Edition 1 2011
1.0 Introduction The power system in New Zealand uses circuit breakers (CBs), disconnectors, earth switches, reclosers, and sectionalisers. These are used to control the flow of electricity, to provide safe isolation and to protect equipment connected to the system. The term used to cover all devices listed above is switchgear. This manual will discuss each of these components. Switchgear forms a critical part of the power system. They are used throughout the system to control the flow of electricity by connecting/isolating the generators, transformers and lines that supply the electricity to the transmission and distribution networks. They are also used within the transmission and distribution networks to control the flow of electricity and to connect/isolate different lines within the networks and to connect and isolate the loads to the transmission and distribution networks.
1.1 Rating The rating of switchgear is defined by the following: Nominal voltage The term nominal voltage, also called voltage class, is used to define the rated system voltage for which the circuit breaker is designed to be used. Rated maximum voltage Rated maximum voltage is the maximum continuous voltage for which the circuit breaker is designed to be used. Rated continuous current Rated continuous operating current is the maximum operating RMS current that the switchgear is designed to operate at. Rated fault current Rated fault current is also known as rated short-circuit current or maximum interrupt current. This is the maximum current that the circuit breaker can safely interrupt. It is important that this is set above the maximum prospective fault current of the circuit. Capacitive current rating Switching capacitive loads is hard on the switchgear and can produce switching surges. Some switchgear designs are better suited than others for switching capacitive loads. Most switchgear will state in the rating the level of capacitive switching it is rated for. Impulse voltage This is the rating that gives the switchgear the ability to withstand voltage impulses caused by factors like lightning. Duty cycle Duty cycle is the number of times in a given period that the switchgear can be operated. This may be stated as a time limit (e.g. 3 operations in an hour, or minimum time between operations) or as the number of normal and/or fault operations until maintenance is required.
TAR 12387 | Edition 1 2011
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Explain the terms below in your own words using an example.
Nominal voltage –
Rated maximum voltage –
Rated continuous current –
Rated fault current –
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TAR 12387 | Edition 1 2011
1.2 Switchgear selection Factors that need to be considered when selecting switchgear include: The power factor of the load. Power factor is used to define the relationship between the voltage and the current. A power factor of 1 indicates that voltage and current waveforms are in phase (resistive load). As capacitance is added to the circuit, the current will start to lead the voltage. A leading power factor of 0 would indicate that the current leads the voltage by 90 degrees or a purely capacitive load. If inductance is added to a resistive circuit, the current will start to lag the voltage. A lagging power factor of 0 would indicate that the current lags the voltage by 90 degrees or a purely inductive load. Typically, the power factor of a load will be lagging with a value >0.8. When the voltage waveform on a circuit with a power factor
