Elect
Controls & Protection
Area of practice · Donald W. Parnell, PE
Protective relaying, relay panels and wiring, one-line and three-line diagrams, control schematics and metering for air-insulated substations, medium-voltage metal-clad switchgear design, station SCADA and communications, and nuclear instrumentation and control documentation.
Substation P&C
Protection and control within substation design
A great deal of protection and control work was required within the substation design recorded across this site. Every substation Mr. Parnell worked on — the more than forty sites at the City of Austin Electric Utility Department, later Austin Energy, and the utility and manufacturer projects that followed — carried its protection and control package alongside the physical design: the relaying that detects faults and trips the breakers, the control circuits that operate the equipment, the metering that measures the station, and the wiring that connects all of it through the control house. The physical yard is described under Substation Design; the protection and control content is recorded here.
Air-Insulated Substations
Substation design at an equipment manufacturer
At ABB in Raleigh, on the Centennial Campus, Mr. Parnell worked in substation design for air-insulated switchgear installations — conventional outdoor substations in which the high-voltage equipment is insulated by air clearance rather than enclosed in gas-insulated modules. Design work at a manufacturer covers the station one-line and three-line diagrams, the physical arrangement of breakers, switches, transformers, and bus, and the protection, control, and metering panels that ship with the equipment, with schematics and wiring diagrams produced to the customer utility’s standards.
Protective Relaying
Relaying for an investor-owned utility
Under contract to Carolina Power & Light, now part of Duke Energy, Mr. Parnell worked in protective relaying. Relaying work at a utility defines the zones of protection for lines, transformers, and buses; selects and applies the relays — overcurrent, distance, differential — that cover each zone; and documents the current- and voltage-transformer circuits, relay panels, DC control schematics, and trip and close wiring by which a detected fault becomes a breaker operation. The same CP&L engagement extended into the nuclear work recorded below.
Medium-Voltage Switchgear
Metal-clad switchgear as a self-contained protection and control system
At Square D, Mr. Parnell worked on medium-voltage switchgear design. Metal-clad switchgear is a complete protection and control system in a single enclosure: each cubicle contains a drawout vacuum or air circuit breaker, the current and potential transformers that feed its relays, the protective relays and control devices on its front panel, the bus and cable compartments it switches, and the secondary wiring, control power, and interlocks that make it operate safely as a unit. Designing a lineup therefore exercises every element of protection and control at once — the one-line, the relay and metering selection for each breaker, the CT and PT ratios and connections, the control schematic for close, trip, and interlock, and the point-to-point wiring of the cubicle — packaged so that the gear can be installed, tested, and energized as a self-contained device.
Projects included switchgear for people-mover systems, where the gear supplies and protects the traction and auxiliary power of an automated transit line under the reliability and fault-isolation requirements of a passenger system, and switchgear lineups for various substations, where metal-clad gear serves as the medium-voltage distribution section of the station below the power transformers. The electromechanical side of this work — operating mechanisms, racking, and enclosure design — is described under Machine Design; the protection and control content belongs here.
Diagrams and Panels
One-lines, three-lines, schematics, relay wiring, and metering
Across assignments for ABB, Patrick Energy Group, Siemens, and Duke Energy, Mr. Parnell produced the drawing set through which protection and control is designed and built: one-line diagrams establishing the station’s electrical arrangement and protection zones; three-line AC diagrams carrying the phase-by-phase current and potential circuits from the instrument transformers to the relays and meters; control schematics for breaker and switch operation, interlocks, and annunciation; relay panel layouts and point-to-point wiring diagrams; and metering panel designs for station and revenue metering. These drawings are the record from which the control house is wired and the protection commissioned.
Station Automation
SCADA, RTUs, and control-house communications
Control-house design carried the station’s supervisory control and data acquisition interface: the remote terminal unit that collects breaker status, alarms, and metering from the relay and control panels and passes operator commands back to the equipment, its points list and I/O wiring, and the communications channel — power-line carrier, fiber, microwave, or leased circuit — to the utility control center. The communications side of this work is described under Telecommunications; the control side, where the RTU meets the relay and control wiring, belongs here.
Nuclear I&C
Instrumentation and control documentation at a nuclear station
Through the CP&L contract and Engineering Design Services, Mr. Parnell worked on nuclear instrumentation and control documentation at the Brunswick Nuclear Plant in Southport, North Carolina. Nuclear I&C documentation is maintained under configuration control: instrument loop and control diagrams, the electrical and instrument penetrations through containment, and reactor-cooling system documentation are controlled records that must agree with the plant as built and be revised through the plant’s change process. The facility layouts and containment penetration diagramming from this work are described under Process Piping; the instrumentation and control content is recorded here.
About this record. This site is a working record of professional experience, maintained to verify subject-matter background. Areas of practice are reached from the menu above. The record is expanded as additional work history is documented.
Donald W. Parnell, PE | North Carolina PE No. 33878