Technician Training: Power Basics

Power Basics

o Terminology – Voltage, Power, Current, Phase & Hertz

o Control Panels – Basics, Single or Dual Power

o Pumps – Basics, Phases & Types

o Dual & Single Power Sources

o Sensors & Instrumentation – Signals & Safety

o Valves – Actuated & Solenoid

Terminology

o Voltage - Alternating Current Typically 120, 208-240, 480 VAC

o Voltage - Direct Current Typically 24 VDC

o Voltage AC Phase – Single or Three Phase (1 PH / 3 PH)

o Voltage AC Hertz – 60 HZ (US) and 50 HZ (INTL)

o Power – US is Horsepower (HP), INTL is Watts (W)

o Current – Amps or Milliamps (A, mA)

Control Power

o Control Panel Power US 120VAC – 1Phase – 60HZ

o Control Panel Power INTL 230VAC – 1 Phase – 50 HZ

o Transform within the Panel to 24VDC for Sensors and Control Relays

o Signal wiring between panels and devices may be 120VAC or 24VDC 120VAC may allow for combining light and signal power within

common conduit and also minimize voltage drop 24VDC preferred for sensors

Control Panel

o Single or Dual Power Drop to Skid

Some designs require a single or dual power feed, typically 480VAC-3Phase, to an equipment assembly

In this case all power management and distribution is done internally to the control panel

The panel will likely include additional power transformers and circuit breakers for this purpose

Pump Power

o Pump Power US Standards

< 1 HP is 120VAC/1 Phase/60Hz

> 1 HP is 480VAC/3 Phase/60Hz

Submersible Pumps is 208VAC/1 Phase/60Hz

If 3 Phase is not available, 208VAC/1 Phase/60Hz

Sometimes there is an alternate 3 Phase, 208 to 230VAC/3 Phase/60Hz

o Pump Power International Standards

< 1 HP is 230VAC/1 Phase/50Hz

> 1 HP is 480VAC/3 Phase/50Hz

Dual Power Source

o Most critical fuel systems have dual power sources for redundancy

o It is important to manage these sources so that they are independent from each other

Monitored with control panels by auto-switching, if A fails then B engages – typically without any effect on the controllers

o Valve & Pump Control for Dual Power Source

Some systems are designed to allow for either of two redundant control panels to operate a single device such as a valve or motor starter

o These are important difference from Service Station systems which often allow for the assumption that control devices share a common power source

Sensors and Instrumentation

o Power is typically 24VDC

Standard wire is often used for level sensors

More sensitive instruments may require twisted and shielded cables for single integrity

Sensor and Instrumentation wiring should be in separate conduit from AC wiring

o Looped Powered Sensors

Some sensors require a separate power source from the signal wiring

Other devices are loop powered, where only 2 wires are needed with power and signal conveyed along a common path

Leak Sensors

Flow Switches

Sensors – Signal Type

o ON-OFF signals are typically 24VDC with a small amperage determined by the load

o Analog signals are either variable voltage, 0-10VDC output, or variable current commonly 4-20 mA output (24VDC)

o Pulsed data signals are also used for certain types of transmitters, typically with some type of proprietary characteristic

Sensors – Intrinsic Safety

o Sensors used in hazardous electrical areas may be either explosion-proof or intrinsically safe

Explosion proof – designed to contain the energy of an explosion or a flammable liquid/vapor

Intrinsically Safe – Limit the energy within the hazardous area to an amount insufficient to cause a spark

The device has low energy requirements, the source panel has an intrinsic barrier to limit the energy conveyed to the sensor, and the conduit/wire systems is isolated for non-intrinsic safety wiring.

Valves

o The most common actuated valves are electric actuated

Pneumatic actuated valves are not practical due to the lack of a reliable dry air source

o Solenoid Valves are commonly used for ON-OFF flow control

Benefits: fail-safe closed & operate simply

Downfall: require continuous energy in some applications which will shorten their life & significant power requirements and amp draws that may exceed the fuse limits

Typically 120VAC, 240VAC, or 24 VDC

De-energized/Energized coils in the solenoids can create a power surge that can damage the PLC or other control interfaces, for this reason they are isolated by relays

Valves (cont.)

o Actuated Ball Valves & Butterfly Valves

Electric actuators used for quarter turn valves are usually 120VAC (sometimes 24 VDC & 240 VAC)

Valve torque specification needs to be matched with actuator torque capacity

Benefit of actuated valves is that there is no power required to maintain the valve position (unlike solenoids) open or closed; valves typically have limit switches for position feedback

Limit switch feedback in many actuators is the line voltage

If 24VDC feedback signals are required the actuator may need to be ordered with auxiliary limit switches