MV SWITCHGEAR SAFETY PROCEDURE

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MV SWITCHGEAR SAFETY PROCEDURE

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MV SYSTEM
Testing & Commissioning SAFTY PROCEDURE
11 Page No. 1 of
Prepare d By: Ramadan Mohamed Naguib DOC REF: MVTC -SAF-000-00
CLASSIFICATION: CONFIDENTIAL
1. General
From the safety point of view, the testing & commissioning of distribution and transmission
plants is often done under hazardous conditions. The risk of accidents must always be taken
into consideration and the testing & commissioning personnel have to be fully aware of the
dangers that exist and should know how to conduct their work to avoid such hazards.
2. Electric shock
Without any doubt, the greatest risk associated with the testing & commissioning of electric
plant is that of electr ic shock. Accidents due to electric shock occupy an exclusive position
since t he persons involve d seldom r eceive a ny forewa rning a s the dang er ca nnot be
apprehended by the human senses. For example, brief contact with a “live” part of an
installation, which neither by sound or movement shows any signs of being dangerous, is all
tha t is necessary to cause a serious accident.
3. Working method
The t esting & commissioning of plant quite often has to be accomplished within a very
short space of time and with many people from different companies involved.
There are two potential reasons for accidents which testing & commissioning
personnel must take into consideration:
Stressing situations where action goes before methodic thinking.
Stressing situation during the energ izing sequence etc. when one party is unaware of
the actions taken by the other.

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CLASSIFICATION: CONFIDENTIAL
The t esting & commissioning personnel must never allow themself to be influenced by
customer demands (economic pressure) etc. which can jeopardiz e the safety of personnel.
During all energizing procedures, all orders and instructions regarding operations,
connections, temporary earthing etc. are to be given by the person (customer/consulting
engineer) responsible for the operation of the plant. All contacts between the la tter person
and AB B’s testing & commissioning personnel are, during the energizing sequence, to be
made via one person only (the chief commissioning eng ineer) to prevent fatal
misunderstanding.
Directives regarding the taking of measurements and any required fault-finding procedures
in energized equipment, are to be g iven by ABB’s chief commissioning eng ineer in order to
minimiz e the risk of accidents which can occur when uncertainty arise as to who does what.
All personnel in the vicinity of t he plant must be fully informed of the risks, which are
present when auxiliary circuits of the plant are energised.
4. Customer’s and third party personnel
Quite often, Vendor testing & commissioning personnel are assisted by
personnel employed by the customer and third party , e.g. during supervisory
engagement. In such cases, the testing & commissioning personnel must be
well aware of the fact that they are also responsible for the safety of such
personnel since they personnally take charge of the daily work. This
responsibility implies that the testing & commissioning personnel must
ensure that assisting personnel are well aware of the risks involved and of
how they should act to avoid such risks.
A suitable way of informing assisting personnel of the hazards associat ed with testing &
commissioning work is, in addition to oral instructions, to give them the opportunity of
studying this document.
5. Work and operational verifications

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Prepare d By: Ramadan Mohamed Naguib DOC REF: MVTC -SAF-000-00
CLASSIFICATION: CONFIDENTIAL
To ensure the utmost safety when working on or wiring up electrical
equipment, some form of written verification is used. This verification gives
the status of a particular section of the equipment. The two most common
expressions are:
Work verification: A verification that a particular section of a plant is completely isolated
from the power supply, that it is earthed and short circuited to an extent as stated in the
verification. This also implies that the specified status of the section will be maintained until
the holder of the work verification issues an operational verification.
Operational verification: A ve rifica tion tha t a pa rticular se ction of the plant, on which the
issuer of the said verification has been working, is ready for operation. This implies that the
section in question is in a condition as stated in the verification and that all earth
connections and short circuits, made by the issuer of t he verification, have been removed.
The work and operational verifications are often combined to one document, a Work
Permit. A Work Permit is issued as a work verification by the person in charge of operations
and is retained by the commissioning personnel until such time as the requisite work has
been completed and the applicable section of the plant is ready for operation.. The
commissioning personnel then signs the document (Operational Verification) and returns it
to the person in charge of operations.
IF THE CUSTOMER USES THE WORK PERMIT SYSTEM, SUCH A PERMIT HAS TO BE OBTAINED
BEFORE COMMENCING WORK ON A SECTION OF THE PLANT THAT HAS PREVIOUSLY BEEN
IN OPERAT ION.
6. Operational responsibility
The person responsible for the operation of a new plant, and thus he who is responsible for
the safety of personnel, during the time from the commencement of plant energ ization to
when the customer takes over the plant, is not always clearly defined. The fundamental
principle is that the customer is always responsible for plant operation and safety as soon
as energization has commenced.

MV SYSTEM
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Prepare d By: Ramadan Mohamed Naguib DOC REF: MVTC -SAF-000-00
CLASSIFICATION: CONFIDENTIAL
The above implies that the customer is responsible for ensuring t hat, among other thing s,
energized section are cordoned off, locks are fitted to control room doors, cautionary signs
are placed in position and that all other precautionary measures are immediately taken.
Prior to plant energiza tion, t he custome r/consulting engineer is to be informed that Vendor
plant/plant section is ready for operation and that the customer, as soon as energ ization is
commenced, is solely responsible for the operation and safety of the plant. This may be in
contradiction to any contra ct agreement but nevertheless should be observed to make all
parties aware of the prevailing situation.
Despite this, Vendor testing & commissioning personnel must ensure that reasonable safety
measures have been taken by the customer. If the customer lacks a functional organiz ation
and the safety measures are considered as being inadequat e, Vendor testing &
commissioning personnel must ensure that rea sonable mea sures are ta ken, considering at
least his own safety. Exa mple of such measures are:
The cordoning off of ener gized bays in the subst ation.
The cordoning off of energized transformers.
The cordoning off of sections of indoor switchgear that have been energized.
The installation of locks for energized areas, e.g. padlocks for the fence around
capacitor banks. (Keys a re always to be handed over to the customer’s operating
personnel).

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7. Disconnection, temporary safety earthing
7.1 General
Prior to commencing work on a plant section, e.g. a substation, where there
is the slightest risk that the equipment is, or can be, energized, the testing &
commissioning personnel are always responsible for ensuring that the
equipment is “dead”. This can be determined in different ways:
With the aid of a voltmeter. Always used for low voltage but not normally for high
voltage.
By making a visual inspection to ensure that the plant section is completely isolated
from the supply and that all temporary earthing measures have been taken.
If the plant is in operation, the customer is normally responsible for such and for ensuring
that sections are isolated and temporarily earthed. In other cases, it is to the testing &
commissioning personnel interest to ensure that necessary measures have been taken to
ensure their own safety and that of other personnel.
7.2 Disco nnection
A plant section is considered as being completely isolated only when all the conductors,
that can supply power to the section, are disconnected. This is accomplished by means of
disconnectors incorporating visible break points or reliable position indicators, or by the
ext ract ion of fuses, t ruck-type circuit breakers, etc.
When isolating a plant section, certain items must be given special consideration:

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Re verse supply. A great deal of accidents have occurred in cases when the persons
involved were unaware of the fact that the plant was being supplied in the reverse
direction from ring circuits, local auxiliary power generators, etc.
Erroneous action. Always make a careful check to ensure that the correct
disconnec tors ar e opened.
Ina dvertent br eaks. Before operating a disconnectors, always ensure that the load
current (if any) has been interrupt ed since conventional disconnectors are not designed
to break heavy current .
Disconnectors, truck type circuit breakers, etc. are to be locked in their open positions to
prevent them from being closed by mistake.
7.3 Temporary safety earthing
Tem pora ry sa fety ea rthing means the earthing a nd short c ircuiti ng at the place of work to
ensure that the plant section in question will not be subject to any voltages which can be of
danger to the personnel.
Prior to commencing work on a hig h-voltag e installat ion, the lat ter must always be
temporarily eart hed. If fix ed earthing switches, earthing trucks, etc. are incorpora ted,
these are to be used. If portable earthing equipment is used, this must first be connected to
earth and then to the phase conductors. If the plant is “live” by mistake, a powerful arc
can develop when making earth connections. For this reasons, appropriate tools such as
insulated rods are always to be used. Portable earthing equipment must be capable of
withstanding the highest short circuit current for a period of 1 second.
7.4 Barriers
If testing & commissioning work is to be done on a partially energized plant “hot plant”
where the testing & commissioning personnel may inadvertent ly come in contact with a

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Prepare d By: Ramadan Mohamed Naguib DOC REF: MVTC -SAF-000-00
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“live” plant section, barriers, are to be set up to g ive warning of the “live” plant sections
that are located in the vicinity of the place of work. Example of such sections are:
• Near-lying energiz ed bays in indoor and outdoor.
• Energized transformers, thyristor stacks etc.
Even when high-voltage tests are being made on plant sections, the equipment being
tested and the test equipment must be cordoned off to prevent accidents.
Special barriers ropes, fitted with appropriate warning signs are suitable for this purpose.
The ropes should be removed immediately after they have served their purpose.
7.5 Clothing
To reduce the risk of accidents and to minimize the effects of accidents which may occur,
the commissioning engineer should not wear rings, necklaces, wrist-watch straps, etc. of
metal when making tests in which he may come in contact with “live” parts.
Clothes of synthetic material should not be worn if there is any risk that arcs can develop.
Synthetic material melts and penetrates the skin resulting in severe burns and other
injuries.

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8. Measuring equipment and tools
8.1 Fuses
When measuring voltages on distribution busbars (high short-circuit
powers/powerful arcs), great care must be exercised in order to avoid short
circuits. The inputs of the instruments being used must incorporate fuses. If
an output is connected between the phases of a busbar a fatal accident may
be the result.
8.2 Insulated tools
If works has to be done in energ ized low-volta ge switchg ear etc. , the handles of the tools
used must be adequately insulated. If screwdrivers are used, their shank must also be
insulated. One of the most common accidents occurs when a screwdriver slips and its
shank ca uses an undesired short circuit/arc.
9. Induced voltages
Non-energiz ed plant sections, such as lines and busbars in outdoor substations, which are
not earthed, can often assume dangerous potent ial due to induction from near-lying “live”
parts. The risk for dangerous induction voltages is greatest in the vicinity of high-voltage (>
200 kv) substations. The shock received by a person who inadvertently comes in contact
with a part energized by means of induction, for example in an outdoor apparatus, can be
sufficient to throw him off a ladder. Induction voltages in non-operating plants can be
preve nted by ea rthing , e. g. with nor mal copper wir e.

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10. Current transformers
Secondary circuits of current transformers must never be opened while the latter are
energized. If a secondary circuit is opened, the entire primary current will become
magnetizing current and the core will saturate resulting in very high voltage (tenfold kV)
across the secondary circuit. Great care should always be exercised when measuring the
load current in secondary circuits. If a test switch is incorporated in the circuit, a current
metering plug with built-in overvoltage protection is preffered to be used.
11. Voltage transformers
When making injection tests on protective relays etc. which are connected to voltage
transformers, there is always a risk of the latter being supplied from the reverse direction in
which case t hey produce high voltage which is fed to equipment connected to the primary.
When connecting test equipment to voltage circuits, the secondary windings must
therefore always be checked to ensure that they are disconnected in order to prevent any
reverse supply to the transformers.
12. Power capacitors and high voltage cables
Due to their capacit ive charac teristics, capacitors and cables are capable of storing
considerable amounts of electricity energy for lengthy periods of time. B efore touching a
previously energ ized power capa citor or a high-voltage cable, care must be ta ken to ensure
that it is really in the discharged state, i.e. short circuited and earthed (via a discharge
resistor if such is included).

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13. Low voltage switchgear
The short-circuit power in large low-voltage switchgear is often relatively high. The high
power and the relatively long tripping times of the “incoming” short-circuit protections,
during a short circuit, result in a very high current (powerful arcs) for a relatively long time.
If work has to be carried out on an energiz ed substation, the tools used must therefore be
adequately insulated to prevent inadvertent short circuiting.
Voltage measuring instruments such as voltmeter or phase-sequence indicators, which are
used during the testing & commissioning work, are to be connected to the external side of
an apparatus g roup, i.e. on the fused side. Furthermore, the instruments used should,
where possible, be provided with fuses.
14. Batteries
For operational reasons, the station battery of a plant is normally connected directly t o the
DC-distribution board without any intermediate fuses. The high short-circuit current from
the battery is therefore not limited by any fuse and great care must be exercised when
taking measurements and when working on the battery circuit.
15. Convertor
The output current of a convertor is, normally, limited only by the convertor’s current
limiter which often has a relatively high setting. As is the case with the battery, great care
must be taken to ensure that the convertor’ s output port is not short-circuited by mistake.

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16. Fuses
When removing/insert ing high-rated fuses, such as blade fuses in low-voltage switchgear,
or high-voltage fuses, insulated fuse tongs are always to be used.
Where such is possible, fuses should always be replaced in the “dead” state, i.e. with the
fuse-swit ch in the “Off” position. If, for any reasons, the fuseholder cannot be de-energized
(e.g. battery fuses), one should always make a habit of ensuring that no short circuit occurs
when large-size low-voltage fuses are inserted in their holders. The best way of doing is to
check that the voltage across the other fuseholders is zero after inserting the first fuse.
17. Electrically operated equipment
During testing & commissioning when personnel are working on the equipment, g reat care
must always be exercised to ensure that outdoor circuit-breakers, SF6 circuit-breakers,
disconnec tors, mot ors, etc . ar e not opera ted by mist ake. Te nsioned springs tha t ar e
released, rotating shafts, levers and the like, can cause serious injury. The risk of shocks,
and injuries due to falls from ladders, etc, must also be taken into consideration.
Accidents of this type can be prevented by disconnecting the control circuits to electrically
operated equipment and, if possible, by securing such equipment mechanically.