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(b) Operating transformer tap changers and phase-angle regulator tap changers.
(c) The control of valves.
(d) Transmission of set points.
The supervisory equipment not only provides control from the master station, but is used to
transmit position indications and metering from the remote to the master station. Another
common function is the transmission of alarm conditions from the remote to the master station.
6.3.3.2 Old Systems. Until recently, most supervisory systems consisted of relay chains at
the master and remote stations that were operated by pulse codes to select the proper operating
point and then perform the control action. These systems use various pulse codes on either DC
or audio-tone communication channels. Generally, the transmission speed is rather slow and is
suitable for telegraph-grade channels.
6.3.3.3 New Systems. The latest supervisory system uses solid-state components rather
than relays to generate and receive selection and operation codes. They usually operate over
audio-tone channels using frequency-shift-type equipment and are capable of very high operating
speeds. These systems can be operated over any high-speed communications channel including
microwave, telephone, or power-line carrier. Bit rates of 1,000 bits per second or higher are
common. This type of equipment often continuously scans the alarm and indication points.
Telemetering is usually accomplished by converting from analog to digital form at the remote
station and transmitting in digital form, a code similar to that for control being employed. Many
modern installations display the telemetered quantities in digital form at the master station.
Various control sequences and code-checking techniques are used to assure operation of the
correct device and prevent false operation. By using modern equipment, a very high degree of
security is possible.
6.3.4 Automatic Control. Automatic control is a combination of various devices, including
relay operational amplifiers, magnetic amplifiers, and solid-state switches, which are used to
automatically operate devices in generating stations and substations without operator
intervention. Unattended substations are usually designed to operate automatically. The
automatic controls normally provided in unattended stations include automatic circuit
breaker reclosers, transformer tap changers or voltage regulators (to control voltage), and
capacitor switches.
6.4 SAFETY AND ENVIRONMENTAL REQUIREMENTS. This section provides a
discussion of the safety practices, environmental regulations, and occupational safety and health
requirements that apply to the operation and maintenance of electric power distribution systems.
Safety and health standards are prescribed by OSHA (29 CFR 1910) and the National Electric
Code (ANSI/NFPA 70). OPNAVINST 5100.23B specifies program requirements and
establishes standards for the safety and health of Navy employees. Activity Safety Offices
6-8





 


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