Hong Kong Regulations

ELECTRICITY SUPPLY REGULATIONS - REGULATION 39

Special regulations as to extra high pressure

EXTRA HIGH PRESSURE

(1) This regulation shall have effect in the case of a supply at extra high
pressure, and shall be in addition to and not in substitution for the
obligations imposed by the foregoing regulations.

(2) An extra high pressure main shall not be brought into use unless, after it
has been placed in position and before it is used for the purposes of supply,
the insulation of every part thereof has withstood the continuous application,
during half an hour, of pressure exceeding the maximum pressure to which it is
intended to be subject in use, that is to say, in the case of every electric
line to be used for a pressure not exceeding 10000 volts twice the said
maximum pressure, and in the case of a line to be used for a pressure
exceeding 10000 volts, a pressure exceeding the said maximum pressure by 10000
volts; and the company shall record the results of the tests of each main or
section of a main.

(3) Every extra high pressure main shall be protected by a suitable fuse or
automatic circuit-breaker, but in the case of a concentric main that fuse or
circuit-breaker shall not be inserted in any external conductor thereof which
is connected with earth.

(4) In every case where an extra high pressure supply is transformed or
converted to a reduced pressure, some suitable automatic and quick-acting
means shall be provided to protect the reduced pressure circuits from any
accidental contact with or leakage from the extra high pressure system, either
within or without the transforming or converting apparatus.

(5) All metal conduits, pipes or casings containing any extra high pressure
electric line shall be efficiently connected with earth and shall be so
jointed and connected across all street boxes and other openings as to make
good electrical connection throughout their whole length.

(6) Every portion of any extra high pressure electric line placed above the
surface of the ground, otherwise than in a sub-station, or in any subway not
in the sole occupation of the company, shall be completely inclosed either in
a tube of highly insulated material embedded in brickwork, masonry or
cement-concrete, or in strong metal casing efficiently connected with earth.

(7) (a) Where extra high pressure mains for three-phase supply consist of
insulated conductors laid together, provision shall be made to ensure that
neither the ground nor any neighbouring or electric line or conductor can
become charged by leakage from any such main.

   (b)  Where this provision is made by a copper strip under a lead sheath
        that strip shall be not less than sixteen-thousandths of an inch in
        thickness, and where it is made by steel wires outside a lead sheath
        each of those wires shall be not less than one-tenth of an inch in
        diameter.

   (c)  Where the mains are inclosed in a lead sheath the sheath shall be not
        less than one-tenth of an inch in thickness and shall be permanently
        and efficiently connected with earth.

(8) Extra high pressure mains for single phase supply and all cables connected
therewith shall consist either of 2 concentric conductors or of separate
conductors. Where concentric conductors are used the insulation shall be
maintained efficiently throughout except that the outer conductor shall be
connected with earth at 1 point, and where separate conductors are used
provision shall be made as in the case of mains for three-phase supply to
ensure that neither the ground nor any neighbouring electric line or conductor
can become charged by leakage.

(9) An extra high pressure electric line shall not be brought into use for the
supply of energy before it has been completely laid, properly jointed,
examined and tested or until it is in the sole charge of the company, and
every such line shall during its use be in the sole charge of the company.

(10) Extra high pressure mains shall not pass through the same street box with
other mains, unless they are inclosed in strong metal casing; and street boxes
containing high pressure mains shall not contain pipes for water, gas or other
service, or electric mains belonging to another undertaking: Provided that any
such street box may contain telephone wires belonging to the company.

(11) Sub-stations supplied at extra high pressure shall be established in
suitable places and shall be in the sole occupation of the company.

(12) Sub-stations constructed below the surface of any street after 2 December
1921, to which an extra high pressure is to be given shall not contain
switches or apparatus other than transformers.

(13) The transforming apparatus at any sub-station supplied at extra high
pressure shall be so arranged that there shall be no danger of any mains
connected therewith being charged to any pressure beyond the limits of
pressure for which those mains are intended.

(14) In delivering the energy to a sub-station at extra high pressure the
company shall exercise all due precautions so as to avoid risk of causing fire
on the premises.

(15) All extra high pressure electric lines and apparatus placed in a
sub-station shall be highly insulated and thoroughly protected against injury
to the insulation or access of moisture, and any metal forming part of the
electric circuit shall not, unless efficiently connected with  earth, be
exposed so that it can be inadvertently touched. All such lines shall be so
fixed and protected as to prevent the possibility of electrical discharge to
any adjacent metallic substance.

(16) The Director of Electrical and Mechanical Services shall be entitled to
enter at all times any of the generating stations or sub-stations of the
company supplying or supplied at an extra high pressure, and to make any such
examination and tests of the mains, machines, transformers or other apparatus
in use in those stations as may appear to him necessary, and the company shall
afford all due facilities for any such examination and tests. (L.N. 76 of
1982; L.N. 298 of 1982)

(17) Where any extra high pressure circuit is connected with earth the
connection shall be made at one point only, namely at the generating station,
sub-station or transformer, and the insulation of the circuit shall, except at
that point, be efficiently maintained throughout.

(18) (a) The neutral point of the star winding of each distinct three-phase
circuit, used for extra high pressure, may be connected with earth or may be
insulated. If connected with earth through a resistance, that resistance shall
be sufficiently low to ensure that the fuse or automatic circuit-breaker in
the mains shall act.

   (b)  If the neutral point is not connected with earth a separate
        electro-static voltmeter placed in a conspicuous position in the
        generating station shall be connected between each circuit and earth;
        and if the indications of the voltmeters show that the insulation of
        any of the circuits is faulty, immediate steps shall be taken to
        restore the insulation.