Addressing the need to ensure that substation equipment is in a fully operational state, electric utilities employ various techniques to monitor the status of control components.

In recent years, so-called “smart” digital relays have been replacing the older-style relays that have induction discs with “normally open” and “normally closed” contacts to effect control when a fault occurs on the system.

The digital relays not only monitor the status of the system but also perform self-diagnosis. These capabilities allow the relay to signal dispatchers when a defect in equipment requires attention. Taking a step beyond the digital relays to ensure control circuits are in a constant state of readiness, engineers at Florida Power & Light (FPL, Juno Beach, Florida, U.S.) investigated continuous monitoring using the Control Circuit Status Monitor (CCSM), developed by INCON (Saco, Maine, U.S.).

The CCSM, which differs from a programmable logic controller (PLC), connects to the electrical circuits associated with generation, transmission and distribution equipment for monitoring the operational status of critical control circuits.

Using the CCSM, the operator can monitor and program up to eight inputs using simple ladder logic to activate a Form C alarm contact. The unit, completely configured and programmed, can be daisy chained for additional inputs if required.

Application at FPL

In the past, FPL monitored only the trip circuit in distribution breakers. As customer satisfaction becomes more important, FPL not only is concerned about the breaker's ability to trip when a fault appears but also wants to be sure the breaker closes after the fault clears. To monitor breaker status, FPL established a Station Assessment Program to schedule periodic on-site inspections by station engineers to check potential failures of key components.

The ac power supply had been a source of trouble with station control circuits, therefore FPL considered installing an auxiliary relay to monitor ac power. It was apparent, however, that more than the ac power required monitoring to achieve substation reliability. It was obvious auxiliary relays also would be required for all the other key components.

Instead of investing in an array of auxiliary relays to check the status of equipment, FPL installed a CCSM prototype to assess its capabilities in a Square D Type FVB breaker. When FPL discovered several deficiencies during field installation, INCON produced a second prototype that was installed in a Westinghouse Type R breaker.

The CCSM demonstrated its ability to monitor trip coil integrity, latch-check switches, the “69” switch (safety switch), regulator lockout, TX relay (trip auxiliary), CX relay coil (close auxiliary), 240-V ac close power and breaker status (B contact). Historically, these components required manual and visual checking. Now if a failure occurs, the normally energized alarm relay will drop out after a time delay, sending an alarm to supervisory control and data acquisition (SCADA). FPL can respond by sending a troubleman to the site.

The four basic conditions of the CCSM monitors are: the presence of voltage, the continuity of a circuit or device (coil), the state of a switch contact and the condition of a process variable.

• The presence of voltage. A typical circuit breaker has a spring-charging circuit and motor that operate from a locally fused 125-V dc supply bus. A voltage surge or nearby lightning strike could cause the fuses to open, dropping the dc voltage to the spring-charging circuit. This event disables the breaker from arming for its next operation. Detecting the absence of voltage, the CCSM provides an alarm for maintenance.

• The continuity of a circuit or device (coil). Many critical circuits, at rest for extended periods without use, may be subject to oxidation. The extended rest also may provide the opportunity for field pests to create nesting sites within relay cabinets. When these circuits are called upon to operate, the conduction path required to energize a relay or a trip coil may not be established. For example, the police could make an emergency request to have a circuit de-energized because an overhead line has come in contact with a vehicle. Normally, the line would be opened at the nearest substation. However, if a rodent has built a nest near the control relay, sufficient corrosion may have occurred to render the device inoperable. These circumstances would require a more disruptive backup procedure. In this example, the CCSM would have monitored the circuit by continually detecting a trickle current flowing through the circuit. If this test current is disrupted, the CCSM produces an alarm to call for inspection of the device.

• The state of a switch contact. A typical breaker relay cabinet usually has a lockout switch and a “69” switch, which maintenance personnel use to temporarily disable the operation of the breaker. If inadvertently left in the wrong position, these switches will not allow the breaker to operate correctly. The monitoring system can detect the state of the switches and provide notification for the maintenance necessary to enable the breaker.

• The condition of a process variable. A circuit breaker may have a compressed gas source to extinguish the arc during its opening sequence. The CCSM can detect a leak that gets progressively worse and is difficult to observe; this relieves the compressor of unnecessary operation at a high-duty cycle. A pressure switch can ensure that the pressurized source is ready and available, producing an alarm if the pressure falls below an acceptable level. Additionally, the operator can program the CCSM to delay alarming if the compressor is running, but produce an alarm if the compressor runs for an abnormally long time.

The Function of the CCSM

The basic function of the CCSM is to monitor the operational status of control circuits. An example is a relay coil burning out after a successful operation. While engineers have recognized the problems associated with defective components, the solutions frequently involved the installation of additional relays or indicator lights to sense the condition of key elements in the control circuits. Installing discrete devices is not only expensive, but these devices also represent additional maintenance to ensure they remain operational. Because the CCSM provides for eight inputs, a microprocessor addresses and monitors the key circuit-status points to prevent misoperation of a critical piece of equipment.

An operator can preprogram a logic profile into the unit to generate an alarm when any of the inputs sense an abnormal condition. The input circuits are specialized in several ways. First, they have high impedance and are effectively non-intrusive, allowing circuits to be monitored without affecting their normal operations. Also, they are electrically isolated and have special high-reliability features, including surge protection and internal self-checking. They are insensitive to polarity and assure a reliable output signal.

This flexibility allows connections to be made in parallel with several types of circuits and sensing relay outputs without affecting trip operations. The sensing inputs accept ac or dc over a wide range of voltages with corresponding currents that are low because of the high impedance of the circuit.

An operator can program additional timer and latch functions to prevent alarms during transition events. Each of the eight inputs has a corresponding labeled LED. The alarm relay, with an adjustable time-delay pickup and dropout, will drop if the CCSM loses power, the relay fails or the CCSM fails a self-check.

CCSM Moves into the Future

Electronic control panels and related control circuits are standard equipment in substation systems. Frequently, these circuits do not function for several reasons, ranging from a switch left in the wrong position to a burned-out relay coil, or possibly even a worn-out contact.

As electric utilities continue to adjust their maintenance schemes and personnel assignments, the need for control circuit monitoring devices will grow. These devices will become the eyes and ears of maintenance crews who are responsible for inspecting and monitoring equipment.

The CCSM proved to be beneficial at FPL with its ability to monitor critical control circuits on a continuous basis, reducing its manpower requirements for having to physically visit substations on a predetermined schedule. Instead, a troubleman is dispatched to examine and repair faulty circuits only when warnings or alarms have been issued to indicate the need for immediate corrective action.

Mark Forrest is a protection and control engineer at FPL, where he has worked for 22 years. He earned the BSEET degree from Florida International University in Miami, Florida, U.S., in 1978. Forrest is a registered professional engineer in Florida.

Theory of CCSM Operation

The Control Circuit Status Monitor (CCSM) controls eight inputs that are electrically isolated by means of high-gain optical isolators and surge protected by discharge arresters and metal oxide varistors (MOVs), which exceed the IEEE C 37.90 standard for surge withstand capability (SWC). An 8-bit microprocessor scans the inputs to determine if an alarm condition exists, based on user-programmed logic equations. The alarm delay and latch also perform under software control. The alarm output circuit is an electromechanical relay, which is controlled by programmable functions assigned in the microprocessor software. A fail-safe, capacitive-coupled driver circuit is used to ensure true operation of an alarm signal, even if the microprocessor was to stop operating. Circuit power is provided by a high-efficiency power supply with RFI filtering, which prevents electrical noise from being radiated into the enclosure or into external circuits.

Alarm Logic and Programming

The CCSM can be configured specifically for a particular application with programming that is accomplished by first connecting a terminal or computer to the RS-232 port and then communicating with the unit using simple commands. If a computer is used, a terminal emulation program, such as HyperTerminal, which is included with Microsoft Windows, can be used. All programming information is automatically stored in the CCSM, even if power is interrupted for long periods of time.

The menu structure is a two-level system with Level 1, the base level, containing basic commands for programming and displaying setup parameters. Level 2 commands are specific submenus relating to particular functions relating to input sections (i-menu: one through eight) and another relating to the internal logic relay sections (menu: one through 16). The i-menu input section is programmable as active on or active off, indicating that voltage is either present or not present. Each input has an indicator light, which is visible on top of the CCSM. The lights can be configured to illuminate when the input is active or not. The “light” command, which is used to program this on or off state, is accessible in the menu section and is useful for indicating either the normal or abnormal state of the input logic relays.

The alarm relay is both a physical and logical device. Physically, it is an electromechanical relay with Form C contacts available on the terminal blocks of the CCSM. Logically, it is a programmable relay with 12 available inputs, a timer function and a latch function. Any one of the inputs can be assigned to the CCSM's inputs, either inverted or non-inverted, or to the output of the alarm relay.

The function of the alarm relay provides for a delay of up to 255 sec before an alarm condition is actually acknowledged as an alarm, which allows transition states to take place without tripping the alarm condition. The “outd” command is used to program the alarm delay period and is available in the Level 1 section of the menu.

The alarm output latch function allows the alarm condition to be momentarily remembered, even if the condition returns to the non-alarm condition. This feature is useful in situations where the CCSM is monitored at a slow scan interval. An intermittent alarm condition that lasts for a shorter time period than the scanning interval can still be recorded. The output latch is programmed with the “latcht” command and is available in the Level 1 section. Latch times can be programmed from one to 254 sec, where a zero value is used for no latching function and 255 is used for an infinite latch time.

A power-down of the CCSM will clear an infinite latch condition or the latch can be reset with the “reset” command. The output latch commands are available in the Level 1 menu section. The alarm output can be disabled by applying voltage to the alarm inhibit input, which allows the user to perform maintenance on the monitored equipment without causing an alarm condition. This feature does not require programming.