Glossary terms beginning with S

Terms used within Transpower
Click one of the letters above to go to the page of all terms beginning with that letter.
sacrificial anode

An anode used to protect a structure by galvanic action.

safety distances

These are the distances in air applied in the design and layout of open type high voltage substations to enable persons to carry out work without danger.

safety measures

Measures taken to ensure work can be safely undertaken under an authorisation, e.g. isolation and earthing. They are either issuer applied (applied by or on behalf of an issuer to enable an authorisation to be issued), or recipient applied (applied by or on behalf of a recipient, where appropriate, to safeguard the work party from potential hazards). Note: Earths applied by the work party to transmission or distribution circuits are examples of recipients applied safety measures.Recipient-applied safety measures are applied, where necessary, in addition to those applied for authorisation issue. Safety measures may consist of ensuring that systems such as seal oil and hydraulic oil remain in service, where necessary, for the equipment to be worked on remaining in a safe state for work.[SR-EI April 1995]

safety observer

A competent employee delegated by the supervisor of the proposed work to continuously observe the work party and warn against unsafe approach to live equipment. [SR-EI April 1995].

safety observer required point

A horizontal plane through a tower body equivalent to the MAD vertically below the lowest conductive element. A safety observer is required above the SORP.

safety valve/relief valve

A pressure relief valve, spring or dead-weight loaded, fitted to a pressure vessel or air compressor, to allow air to escape to atmosphere when the pressure exceeds the pre-set safe value.

SC/AC (lines)

Steel conductor, aluminium clad (alumoweld).

SC/CC (lines)

Steel conductor, copper clad (Copperweld).

SC/GZ (lines)

Steel conductor galvanized (GEHSS).


Across flats. This refers to the dimension between the flat, inner faces of a hexagonal die used for compressing compression fittings Steel conductor/ galvanized (GEHSS).


(Supervisory control and data acquisition.) The monitoring and remote control of equipment from a central location using computers.


Standard Communications Alarm Unit.


Service Centre, Christchurch. See Transpower service centre.


Service Centre, Hamilton. See Transpower Service centre.


The SCH Master SCADA installation at SCH.  This receives indications from the FRED Master and issues controls via its man/machine interface.


Single Circuit Pole.

scraping earth

A term used to describe the earth connections between a plug and the case of the socket or connector.


Wild, naturally sown vegetation, plant and tree growth.


A system which provides local operation of the plant from a personal computer, replacing control and alarm panels.

sealed transformer

A transformer which is non-breathing, that is, so sealed that there can be no significant interchange between its contents and the external atmosphere. [BS 171: Part 1: 1978].

sealed tunnel

A cable tunnel that is sealed off and without ventilation to prevent general access and which may contain hazards that may endanger personnel.

sealing end

A term used in this standard to encompass cable sealing ends and pot heads.

secondary distribution panel

A fuse or circuit breaker panel remote from the power supply, located in an equipment cabinet to protect separate equipment circuits.

secondary equipment

Equipment used in control and monitoring the operation of primary equipment, e.g. protection, instrumentation, and metering (see also primary equipment).

secondary surface preparation

Preparation of non-rusted tower steel for primary painting by high-pressure water cleaning.

secondary winding (for instrument transformers)

A winding which supplies the voltage or current circuits of measuring instruments, meter relays or similar apparatus.

secondary winding (for power transformers)

A transformer winding that delivers active power into a load.

section length

Means the distance between the contact surfaces at the top and the bottom of an insulator where the adjoining fittings attach.  Refer toa the relevant specification drawing.


Breaking a conductor or network into sections for the purpose of livening in stages, fault finding, or controlled restoration.


A term used to describe the ability or capacity of a network to provide service after one or more equipment failures. It can be defined by deterministic planning criteria such as (n), (n-1), (n-2) security contingency. A security contingency of (n-m) at a particular location in the network means that m component failures can be tolerated without loss of service.

security broached locking

Security broaching is used as a means of preventing unauthorised duplication of keys.

security coordinator

The Transpower person with overall authority to manage the secure operation of the power system.

security system equipment

Refers to electronic access control and surveillance equipment.

separate cooler

A cooler too large to connect directly onto the transformer tank.

sequence control

A control system that operates and monitors a machine's start and stop sequences, and monitors it while running.

sequential event recorder

A device that records, in chronological order, changes of the state of equipment, with a fine resolution of time.


A device that records, in chronological order, changes of the state of equipment, with a fine resolution of time.

series gap (surge arrester)

This is a magnetically blown (active) gap assembly consisting of a number of individual spark gaps.

series reactor

A reactor connected in series with other equipment to limit the flow of fault current, harmonic currents, or for reactive power compensation.

serious harm

For the purposes of Transpower employees and Service Provider employees as defined in Schedule 1 of the Health and Safety in Employment Act 1992. (a) Any of the following conditions that amounts to or results in permanent loss of bodily function, or temporary severe loss of bodily function: respiratory disease, noise-induced hearing loss, neurological disease, cancer, dermatological disease, communicable disease, musculoskeletal disease, illness caused by exposure to infected material, decompression sickness, poisoning, vision impairment, chemical or hot-metal burn of eye, penetrating wound of eye, bone fracture, laceration, crushing. (b) Amputation of body part. (c) Burns requiring referral to a specialist registered medical practitioner or specialist outpatient clinic. (d) Loss of consciousness from lack of oxygen. (e) Loss of consciousness, or acute illness requiring treatment by a registered medical practitioner, from absorption, inhalation, or ingestion, of any substance. (f) Any harm that causes the person harmed to be hospitalised for a period of 48 hours or more commencing within 7 days of the harm's occurrence.For members of the public in accordance with the Electricity Act 1992, serious harm means:(a) death; or (b) injury that consists of or includes loss of consciousness; or injury that necessitates the person suffering the injury: -(i) being admitted to hospital; or (ii) receiving medical treatment from a registered medical practitioner.

serious injury

Any injury involving electricity that: includes loss of consciousness; or requires admission to hospital or treatment from a health professional.

Service Level Agreement

A SLA is an agreement between two parties (in this case Transpower and another firm) for the specification of services that one vendor supplies to another.

service plan

takes on board the ISSP - high level initiatives and funds assigned from the business plan, takes on board portfolio roadmaps, shows funds distribution across strategic and tactical projects across all portfolios roadmaps and timings, aaddresses dependencies between projects across portfolios.

service requirements sheet

A document which specifies Transpower’s contractual requirements for the service of a specific type of equipment.

service specifications

Are schedules to services contracts.  They communicate Transpower's requirements regarding contract service outcomes and essential process and procurement requirements to contractors and suppliers.

servicing summary sheet

The base document which is used by Transpower for the preparation of service requirement sheets, work guides, and maintenance reports for specific types of equipment.


Severely Errored Seconds

set point command (SCADA)

A command in which the value (set point) for the required state of operational equipment is transmitted to a controlled station where the set point is stored.


SF6 (Sulphur Hexaflouride) is the most potent greenhouse gas, having 23,900 times more global warming potential than the equivalent amount of CO2 (Carbon Dioxide). Transpower holds approximately 80% of the SF6 in the country. The gas is used as an insulator in substations, primarily in gas-insulated switch gear and circuit breakers, although it can be found in other equipment. Transpower, since signing in 2004, is a party to a Memorandum of Understanding between the Government (Ministry for the Environment) and major SF6 users such as Tiwai Comalco Aluminium Smelter and Genesis Energy. Under the agreement Transpower commits to keeping SF6 emissions below 2% of installed nameplate capacity, and to report annually on its SF6 inventory and emissions.

SF6 circuit-breaker

A circuit-breaker in which the contacts open and close in sulphur hexafluoride gas.


System fault and interruption report.

shear disk

A protective device for relieving excess pressures in enclosed containers (e.g. transformers, metal-enclosed switchgear, pressure vessels or air compressors) consisting of a thin disk of corrosion resisting metal, graphite or polycarbonate carefully controlled as to thickness. The disk is designed to burst, giving a large opening for the rapid release of pressure. Also known as burst disk, rupture disk.

shock current (Ib)

The minimum current through a human body which will cause ventricular fibrillation.

short circuit rating

The three second fault rating of equipment.

short term rating

The maximum rating to which equipment can be operated for a specified duration.

shunt reactor

A reactor connected between earth and the live conductors of a power system for the purpose of absorbing reactive power.

shutters (switchgear)

Lockable barriers to prevent access into the spouts of withdrawable switchgear.

SI unit

Systeme International units of measure.

significant hazard

A hazard that is an actual or potential cause or source of: (a) Serious harm; or (b) Harm (being harm that is more than trivial), the severity of those effects on any person depend (entirely or among other things) on the extent or frequency of the person's exposure to the hazard; or (c) Harm that does not usually occur, or usually is not easily detectable, until a significant time after exposure to the hazard. For the purposes of members of the public it includes significant property damage.

single - side

Refers to a duplicated supply switched to supply #1 or supply #2 or an unduplicated supply with one battery disconnected.

single battery system

A station d.c. power supply with one battery and one battery charger.

single side band

A modulation technique used in HF radio. Note: In Transpower, SSB radio equipment is used for the emergency radio network.

single-circuit line

A transmission line carrying one circuit.

single-line diagram

A drawing that shows by single lines and symbols a simplified layout of a three-phase electrical system.

site abbreviation/standard site abbreviation

A three-letter abbreviation that has been allocated to identify sites used in the management, operation and maintenance of transmission and power generation assets. (An exception is Mangahao Lakes where the final digit is numeric.).


A SLA is an agreement between two parties (in this case Transpower and another firm) for the specification of services that one vendor supplies to another.


Single-line diagram.


Safety Rules-Electricity Industry. (Replaced by SM-EI).

SML (lines)

Specified mechanical load.

smoke vent system - FVNT

Term used in this standard to define a system of vents which activate on detection of a fire and which release smoke and heat. The system consists of the vent, the vent control and release mechanism and the control panel for automatic and manual release. Where the vent provides for ventilation functions other than for smoke and fire these functions and their controls and mechanisms are to be included in any servicing requirement.


Supervisory management system.


A horizontal plane through a tower body equivalent to the MAD vertically below the lowest conductive element. A safety observer is required above the SORP.


Switch on to fault. See protection.


Spacings are distances measured between centre-lines of conductors or equipment.


The flaking and splintering of concrete surfaces, usually caused by the rusting of internal reinforcing steel or freezing of water that has entered the concrete. This condition gradually reduces the strength of concrete members.


The gap between two adjacent transmission line towers, poles or structures in which conductors are strung or are to be strung. [Compiled for this glossary].

span length

Means the centre line horizontal distance between two adjacent supports.  (For short spans, when determining the horizontal distance of the fixing points of a conductor, the angle of the crossarm to the line direction, and crossarm or support width, shall be considered accordingly.).

spark gap

A protective device connected in parallel with a resistor bank which permits fault current to start discharging when a predetermined voltage is reached.


Special Purpose Condition Assessment, or where an independent party is engaged to fully assess the corrosion on a tower by detailed measurement.


Scheduling, Pricing and Dispatch. A computer system used to calculate schedules and prices for the New Zealand Electricity Market and the reserves market.

special location

Any area within: School grounds. Children’s playgrounds. Swimming pool areas. Popular beaches or water recreation areas. Public thoroughfares within 100 metres of the above locations.

special purpose assessment

A detailed assessment of one or more specific features of a transmission line, (rather than assessment of all aspects).

specific creepage

A measure of the total surface distance across the insulating part of an insulator from top to bottom, following all the curves in the shed profile. It is effectively the total minimum distance through which leakage current must flow. Usually specified in mm/applied kV to give a relative performance measure.

specified transmission line tower sites

Specific sites located in built-up areas as identified in Annex A of the Special Conditions of Contract.

speed (power system)

The frequency of the power system.

speed governor

A mechanism for regulating the speed of a synchronous generator, during variations in input power or load.

spinning reserve (of power system)

The available capacity of synchronised plant which can provide immediate assistance during a fall in system frequency. [A component of instantaneous reserve.].

spinning reserve sharing

A slow acting but permanent control which complements the frequency stabiliser. It modulates the HVDC power transfer within a +/- 250MW range to nearly equalise the frequency in both islands. Normally enabled.

split bus

A busbar divided into separate electrical sections by an open bus section disconnector, bus section circuit-breaker, or bus coupler circuit-breaker.


The individual appointed to support, advocate and manage the development of a standard.

spot price

The wholesale price of electricity traded in any given half-hour on the New Zealand Electricity Market. [Transpower website glossary].


A hollow cylindrical insulator, at one end of which is a plug contact solidly connected through an insulator into the busbar or feeder/incomer compartment of metal-clad switchgear.


To render equipment incapable of operating by mechanically preventing its movement.

spur circuit

A circuit connected to the transmission system at only one point.

Spur Line

A segment of the network connected to only one other node (examples include ISL-PAP A&B, KEN-MPE).


Safety Rules-Electricity Industry. (Replaced by SM-EI).


Synthetic rosin-bonded paper.


Single side band.

stability event

The occurrence of and recovery from: any transmission circuit fault; any single busbar fault; any fault on a single interconnecting transformer.[GOSP glossary].

stability limit (of a system state variable)

The critical value of a given system state variable which cannot be exceeded without endangering power system stability.Note: For a power system without a fault, this concept is related to the steady state stability of the system. [GOSP glossary - IEC 50 (603-03-10)].

stability margin (of a system state variable)

The difference between the actual value of a given system state variable and its stability limit. [GOSP glossary - IEC 50 (603-03-11)].

stability zone

The operating area situated within the stability limits of the system state variables. [GOSP glossary - IEC 50 (603-03-12)].


Staging and Conversion System. Software which transfers data between COMIT, SPD and TPIX.


A document containing Transpower's corporate knowledge on a stated topic, for  the information and guidance of staff, consultants and contractors.  A standard will specify the approved systems, technical specifications, requirements or procedures used to ensure a minimum level of compliance with legislation or Transpower policy.  A standard links to or contains applicable policies.

standard components (lines)

A component denoted as "S" in the standard. "N" denotes non-standard. "T" denotes test.

standard person

Appendix A of TP.DS 62.01 Spacings and distances in outdoor substations shows the height and reach of the standard person.  This was derived from British and IEC standards and was based on a 95 % confidence leve of men not exceeding 1890 mm.  Today the population tends to be taller than the previous generation so the proportion of people exceeding 1890 mm will exceed 5 %.

standby reserve

The reserve which can be made available within 15 minutes of receiving instructions from the grid operator. Such reserve must be able to be sustained for at least six hours. [GOSP glossary].

star-delta starting

The process of starting a three-phase induction motor by connecting it to the supply with the stator winding initially connected in star, then reconnected in delta for the running condition.


A particular type of static var compensator, in which power electronic devices such as GTO's are used to generate the reactive power required, rather than capacitors and inductors.

Static VAr compensator

A particular type of static var compensator, in which power electronic devices such as GTO's are used to generate the reactive power required, rather than capacitors and inductors.


A general term to cover substations, power stations and switching stations. It includes switchyards. Note: This term does not apply to ground-mounted distribution substations, pole-mounted substations, kiosks and radio repeater sites, reclosers, disconnectors and sites of a similar nature. [SR-EI April 1995].

station areas

Areas within a station are designated by Transpower as: A public area, A restricted area, A switchyard, A controlled area.

station d.c. system

A d.c. system which supplies predominantly non-continuous and momentary control and protection loads which are large in comparison with the continuous load. The nominal distribution voltage is 125 V.

station earthing

Earths applied to a transmission circuit at the terminal stations.

station side

the Transpower equipment side of the barrier isolation cabinet.


The stationary windings in a generator.

steady state stability (of a power system)

A power system stability in which any disturbances occurring have only small rates of change and small relative magnitudes. [GOSP glossary - IEC 50 (603-03-02)].

steering diodes

Diodes which isolate the two halves of a duplicated power supply.

step voltage

The voltage experienced by a person during earth faults.

Step voltage (Vs)

The difference in voltage experienced by a person bridging a distance of 1 metre with the person’s feet apart, without contacting any other earthed object.

stop valve /cocks

Devices designed to regulate the flow of air (fluids) through an opening or pipe.

stored energy operation (circuit-breaker)

An operation by means of energy stored in the mechanism itself prior to the completion of the operation and sufficient to complete it under predetermined conditions.

strategic technical roadmap

> strategic initiatives, timings and technical ownership > strategic initiatives where A&S (IT Strategy & Architecture) is the sponsor (e.g. Enterprise Arthitecture Tools, Enterprise Application Integrations Tools, etc) - those initiatives belong to the Enterprise Solutions Road Map.

strict liability

Where an employee is personally responsible under environmental law for incidents of pollution or exceeding the conditions of resource consents that are the result of that person's actions or decisions. Such liability cannot be limited by contractual means.

string insulator

Means composite polymer string (long rod) insulator.

structure (lines)

Any tower or pole irrespective of its physical construction, including all insulators and insulator fittings, which forms part of a transmission line.

structure (station)

The assembly of posts, gantries and earthed metalwork which supports items of equipment.

structure reconditioning

Work other than inspection and repair, which involves replacement of significant equipment such as disconnectors, insulators, conductors, and hardware, or corrosion repairs and mitigation measures. It may also include structure modifications and removal of redundant equipment and replacement of feeder protection.


crop harvesting residue.

sub-grid lines

Non core-grid lines which are not the only supply to a particular load.

sub-system testing

Inspections and tests carried out prior to connecting untested equipment to the power system.


A building, structure or enclosure incorporating equipment used principally for the control of the transmission or distribution of electricity.

substation control system

A system which provides local operation of the plant from a personal computer, replacing control and alarm panels.

substitute meter

A meter connected in place of a permanent meter to allow testing, maintenance or replacement without loss of revenue metering capability.

sulphur hexafluride gas (SF6)

A gas with very good dielectric properties, used in electrical equipment.


The employee who is in charge of the work at the place where it is performed. [SR-EI April 1995].

supplementary operating form

An extra operating form used when additional items are required when actioning an existing operating sequence.

supplied air respirator

A full faced mask with pressure feed air supplied from an external source.


The person/organisation which supplies, imports, sells, or hires pressure equipment or cranes and includes Transpower when it directly imports any pressure equipment or crane into New Zealand for its use, or sells any pressure equipment or crane.


The provision of electricity to a network operator or a direct consumer.

supply bank

A 3-phase transformer or group of 3 single-phase transformers, connected to a HV bus for supply from the secondary windings.

supply voltage

The voltage range over which the equipment being supplied by the d.c. system is designed to operate.


Means the total structural system used to support an overhead line at a particular location, and includes such elements as foundations, poles, steelwork, stays, struts, crossarms and fittings.

support brackets

Fabricated steelwork bolted to the tower cross-arm to which the hanger bracket is attached.

surge (system)

A sudden fluctuation in voltage and/or frequency typically occurring during a system fault.

surge arrester

A device designed to protect electrical apparatus from high transient voltages, they are connected between the electrical conductors of a network and earth to limit the duration and frequently also the amplitude of following current.

surge counter

A device that counts the number of current impulses through the surge arrester.

surge impedance

The surge impedance of a conductor is a mathematical constant, approximately equal to the square root of the quotient of the inductance of the conductor and the capacitance between the conductor and ground.

surge relay

A relay placed in the oil line to detect surges in the oil and provide a trip in response to a fault. Usually placed between the tap-changer diverter switch and tap-changer conservator and sometimes on smaller transformers between the tank and the conservator. (Related term: gas-operated relay).

suspicious tripping

A circuit-breaker operation which cannot reasonably be attributed to weather conditions or any other known conditions existing at the time. Note: An otherwise suspicious transient fault on a circuit with a history of similar unexplained transients faults is not considered a suspicious tripping unless the tripping is in some way uncharacteristic of the previous tripping (e.g. occurs in a different time period or climatic season etc.).


A particular type of static var compensator, in which power electronic devices such as GTO's are used to generate the reactive power required, rather than capacitors and inductors.

switch (noun)

A mechanical device capable of making, carrying and breaking electric currents.

switch (verb)

To operate switchgear.


A collective term for switches of all types and their associated equipment, including circuit-breakers, disconnectors, and earthing switches.

switchgear group

A circuit-breaker and related disconnectors. The relationship is determined by switchgear numbering.

switchgear number

A composite number used to identify an item of switchgear which is under the control of an operator. The number is encoded to identify the switchgear group and the equipment function.


Operations involving the opening or closing of switchgear.

switching station

A station which exists solely for the purpose of transmission rather than supply.

switching unit

An item of outdoor metal-clad switchgear, used on a network.


An area, enclosed by a security fence, containing normally live conductors and/or other exposed live material. [SR-EI April 1995].

swivel pin

Bolt or double-ended stud used to attach the hanger bracket to the tower support brackets.

sync. Check

A feature that applies to some auto-reclose schemes whereby auto-reclose will only occur if the voltages on both sides of the circuit-breaker have the same frequency, detected by ensuring the voltages are within a pre determined magnitude and angle for a pre-determined time.


To adjust the frequency, voltage and phase angle of an a.c. machine (or part of the power system) to match that of another machine (or part of the power system) in preparation for closing the circuit-breaker between them.

synchronising point

A station provided with facilities to synchronise adjoining parts of the system.

synchronous compensator

A synchronous machine running without mechanical load and supplying or absorbing reactive power to regulate local voltage.

synchronous condenser

A synchronous machine running without mechanical load and supplying or absorbing reactive power to regulate local voltage.

synchronous operation of a machine

The ideal operating condition of a synchronous machine connected to the network in which the electrical angular velocity of the machine corresponds with the network frequency. Under practical operating conditions the angular velocity of the machine may slightly oscillate around the ideal value. [GOSP glossary - IEC 50 (603-03-13)].

synchronous operation of a system

The condition of a system in which all machines are in synchronous operation. [GOSP glossary - IEC 50 (603-03-14)].

synchronous speed

The speed of rotation of an ac machine which results from the frequency of the system to which the machine is connected and the number of poles in the machine.

synchronous time

The time kept by a synchronous clock.


An instrument used to indicate synchronism of two a.c. systems.


Any computer system, mainframe, workstation, PC, LAN.

system coordinator

The person with overall responsibility and authority to manage the secure operation of the power system.  Together, the security and evergy co-ordinators perform the real-time roles of the system operator.

system frequency

At any instant the value of the frequency of the power in the North Island or South Island. See also Hertz, nominal system frequency [Also frequency].

system minute

As an overall measure of performance, Transpower records non-delivery of electricity in system minutes. The system minutes are calculated by dividing the amount of energy not supplied by the maximum demand for the year. [Transpower website glossary].

system normal

The power system is operating in the normal state when: Generation meets the demand at 50Hz (±0.2 Hz). Voltage requirements are met. Grid equipment is operated within design ratings. Reserve margins and the power system configuration provide an adequate level of operational security.

system number

A coded number assigned to specific equipment for the purposes of operating the grid that, when used in conjunction with a locality name, uniquely identifies the equipment. [GOSP glossary].

system operator

The person responsible from time to time for the operation of the grid system. The system operator is Transpower New Zealand Limited.

system operator standing instructions

Documentation provided and published by the system operator from time to time describing specified details of the process by which the sytem operator and dispatch customers meet the requirements of the Co-ordination Policy.

system speed

At any instant the value of the frequency of the power in the North Island or South Island. See also Hertz, nominal system frequency [Also frequency].

system state variables

The variable quantities associated with the electrical state of a system. Examples: voltages, currents, powers, electric charges, magnetic fluxes. [GOSP glossary - IEC 50 (603-02-02)].

system test

A test conducted on equipment, with that equipment connected to the New Zealand power system, to assess the interaction of that equipment with the grid. [GOSP glossary].

system tests

Tests applied to equipment while it is connected to the power system.

system time

See synchronous time.


Hardware and software systems used by Transpower in the delivery of its transmission services e.g. market, metering, information, communication, control and management systems.