492

THE COLLIERY GUARDIAN.

March 5, 1915.

nected to opposite sections of the busbars. The
generators are protected by balanced protective trans-
formers connected between the neutral and each phase,
and by time-limit, overload, and reverse current devices.
The feeders are protected on the Merz-Price system and
by time-limit overload apparatus.

Fig. 14 shows the method of grouping the busbars,
generators, and switches at the Penallta station, either
generator being able to maintain the supply to each

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Fig. 13.—Diagram of Middle
Duffryn Switchgear.

Figs. 15 and 16.—10,000-volt Switchgear, Penallta and Britannia Collieries.

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point of the feeder network when the busbans are split
for repairs. The switchgear in this station is mechani-
cally operated by levers, the switchgear being in the
basement (see figs. 15 and 16). The generators are
protected by time-limit, overload, and reverse current
relays, the feeders by time-limit overload, and the over-
head, transmission lines and transformers by time-limit
overload and the Merz-Price system.

At the Britannia Colliery the switchgear is erected in
an annex to the winder house,-as shown in figs. 15
and 16, the switches being mechanically operated and
the control pillars being on the floor level. The busbars
are arranged as a ring, which can be separated into'two
halves by 400-ampere oil switches, each section of the
ring being again divisible for repairs by unbolting links.
When the ring busbar is divided, each section of the bar
has direct connection with the Penallta and Bargoed
stations, and a supply can be given from either section
of the busbars to one main winder and to the 10,000-
3,000-volt transformers which supply the remainder of
the colliery plant. The 3,000-volt busbars are treated
in a similar manner. In the first instance the supply
was given to each section of the busbars by one 1,000
k.v.a. transformer. This equipment is now being
increased to two 1,000 k.v.a. transformers per section.

In the Bargoed switchgear (fig. 14) the busbars are
in duplicate, the generators and feeders being connected
to either of the busbars through interlocked isolating
switches. The busbars are in screened chambers,
erected on the main engine room floor level, the switch-
gear and operating platform being 9 ft. 6 in. above the
main floor level, as shown in figs. 17 and 18. The
protective arrangements are as follow :—Generators :
time-limit overload and reverse current relays. Feeders :
time-limit overload and Merz-Price protective system.

The pressure is controlled at the power station by
Tirrill regulators. This has resulted in an improved
power factor on very fluctuating loads. Having regard
to the variation of 25 per cent, in load in either valley
in a few seconds, it was found difficult to maintain a
satisfactory pressure until the plant at the various
power houses was controlled by these regulators.

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Fig. 17.—Bargoed Switchgear.

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The power factor varies between the following limits :

Aberdare Valley ............ 0’7	to 0’85

Khymney Valley ............. 0’7	,, 0’8

The generators are constructed so as to give their full
output with a power factor of 0’75. Owing to the
moderate distance of transmission, there has been no

difficulty in maintaining the normal pressure at the
individual collieries, but in order to deal with further
extensions some of the larger motors will probably be
fitted with power factor correctors.

(b) Motors.—Originally all motors were controlled by
screened panels, the high-pressure parts being protected
by earthed metal screens, interlocked with the isolating