Technician Training: Power Basics

1. Technician Training: Power Basics

2. 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

3. 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)

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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

10. 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.

11. 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

12. 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