The silicon-carbide valve arrester has an element with nonlinear
volt-ampere characteristics which limits the follow current to a value that
the series gap can interrupt. This type is being phased out by manufacturers.
The metal-oxide varistor type arrester provides the most modern
solution to the problems resulting from surge voltages, since its gapless
construction means there is no volt-time-gap sparkover characteristic to be
188.8.131.52 Additional Requirements.
Refer to MIL-HDBK-1004/6 for additional
metering and relaying requirements of MIL-HDBK-1004/3.
184.108.40.206 Energy Monitoring. Check local energy monitoring requirements to
instrument transformers belonging to a utility company cannot be used for
monitoring. Watthour meters at distribution substations should be of the
pulse initiator type. At utilization substations, it is suggested that
watthour meters be provided with the pulse initiator feature, as the cost is
not excessive. While the use of instantaneous and peak demand wattmeters for
all transformers larger than 500 kVA is recommended, actual provisions should
be those required by the activity. As a minimum, always provide at all new
distribution substations, conduit installed to the location selected for a
future monitoring panel from the following points:
energy sensing instrument transformers,
a 120 V power source, and
a communication line tie-in.
220.127.116.11 Control Cables. For control cables refer to IEEE No. 525, Guide for
the Selection and Installation of Control and Low-Voltage Cable Systems in
Substation Working Space and Access Requirements. Design indoor and
outdoor substation layouts to provide safe working space and access to meet
the requirements of NFPA 70 keeping in mind any need for installing and
removing equipment, vehicle access necessary for outdoor substations, and
adequacy of floor or foundations to support equipment weights.
Design. Allocate adequate space early in the programming/planning
stages. Future expansion space should be clearly delineated as should safety
exit requirements. Interior space for substations is always at a premium,
which can be further minimized by the intrusion of structural elements or
installation of mechanical equipment. Electrical requirements are often