Optional Equipment

Three-phase CTs are only available on the load side of the switch. Donut-style or split-core type CTs may be used for line-side applications.

Three-phase Current Transformer

HVL/cc uses a 3-in-1 molded current transformer (see Three-phase Current Transformer) as standard for metering applications in the switchgear. The molded CT is ideal for main or feeder switch applications and is mounted on the load side of the switch. The 3-in-1 molded CT is not available for units fused with the Mersen CS-3 fuses.

For applications requiring CTs on the line side of a switch, donut-type CTs are used in lieu of the 3-in-1 molded CT. Field installable, split-core style CTs are also applicable for line-side CT applications.

This HVL/cc Main-Main automatic transfer scheme is unique in that it does not require voltage or current transformers to initiate the transfer operations. It operates with the RCV 420 transfer relay specially designed for use with the Live Line Indicator bushings in the HVL/cc switchgear. These LLI bushings have internal capacitive circuits that supply the voltage information to the relay. All that is required is control power to operate the HVL/cc switches and the transfer relay.

• Control Power: 24 or 48 Vdc control power is preferred, but AC is also acceptable. When using AC control power, a DC power supply device is supplied for the transfer relay. Also, on all motor operated HVL/cc switches, the motor, close, and trip circuits must all be the same control voltage.

• Automatic Transfer with External Control Power: Automatic transfer can be accomplished with two switch sections if control power is supplied externally to the switchgear.

• Description of Operation: When two HVL/cc main switches are supplied from two different sources, there is a preferred source and an alternate (standby) source. The RCV 420 transfer relay is designed to transfer the load from the preferred source to the alternate source if a lost/low voltage condition occur on the preferred source. The system automatically transfers back to the preferred source when normal voltage conditions are restored. The manual controls use operator-actuated control switches for transferring loads locally in the manual mode.

• Modes of Operation:

  • Automatic operation is defined as opening or closing the main switches by means of an RCV 420 relay. The RCV 420 relay monitors the voltage condition and prompts the OPEN/CLOSE circuits of the switches. This is called unsupervised operation.

  • Manual operation is defined as:

    • Opening or closing the main switches by means of the manual control switches located on the control panel.

    • Opening or closing the main switches by means of the manual push buttons located on the mechanism front panel.

• Protective Interlocking:

  • This system is electrically interlocked to help avoid parallel connection of the two main switches when in the automatic or manual mode:

    • In the automatic mode, electrical interlocks help avoid parallel connection of the two main switches when an automatic transfer takes place.

    • In the manual mode, electrical interlocks help avoid parallel connection of the two main switches when closing either main switch with the manual control switch.

  • Key interlocks are not provided on the main switches.

    NOTE: Electrical interlocks can be bypassed to allow for manual operation of a parallel connection (closed transition).

• Transfer Sequences:

  • Automatic Transfer

    1. The preferred source main (PSM) switch is closed, and the alternate source main (ASM) switch is open during normal automatic operation. If a low voltage condition occurs on the preferred source, it is detected by the relay from the voltage sensors connected on the line side of the switch.

    2. The PSM switch opens on loss of voltage after a time delay (adjustable from 0.1-2 seconds). If the alternate source is available (RCV 420 relay settings are satisfied), the ASM switch closes automatically as soon as the PSM switch is open (open transition).

    3. When the preferred source again becomes available, an adjustable timer (five seconds-two minutes) begins timing to allow the restored source to stabilize. When timed out, the ASM switch opens. The PSM switch closes as soon as the ASM switch is open (open transition).

       NOTE: A test pushbutton is available on the RCV 420 relay to test the automatic transfer per descriptions 1, 2, and 3 above.

    4. Operating the manual control switch when in the automatic transfer mode results in main switch operation in the OPEN (O) position only.

       Exception: When the manual control switch is used to open a main switch while in automatic transfer mode, automatic operation is not disabled (initial startup settings must be reestablished) and an unsupervised main switch operation may occur, depending on source availability.

  • Manual Transfer If control power is available, the main switches can be operated manually using the control switches located on the control panel. These switches operate the main switches when the auto/manual selector switch is in the manual position.

Control Schematic for Preferred Source Switch

Control Schematic for Alternate Source Switch