Electrical and Hydraulic Safety Training Flashcards

Hydraulic Systems

• Solar technicians primarily deal with liquid cooling systems rather than high-pressure hydraulic systems.
• Liquid-cooled inverters use an ethylene glycol and water mixture, similar to a car's engine cooling system.
  • The mixture is pumped to electronics that get hot, stripping the heat away.
  • Heat is transferred to a radiator and recirculated.
• Components include pumps, valves, expansion tanks, electronic valves, pressure gauges/sensors, radiators, and fans.
• System pressure is very low, around 0.55 bar (approximately 2-3 psi), which is less than many car systems.
• Pneumatic systems might be used for stabilizers on tracking systems (gas struts or air springs).
• Most inverters are air-cooled, making liquid-cooled inverters and certain battery types exceptions.
• ABB stuff and some wind inverter technologies still use liquid cooling.

Foundational Electrical Concepts

• Electricity is the flow of negatively charged electrons moving from atom to atom.
• Conductors facilitate this movement, and voltage (potential difference) pushes the electrons.
• Conventional Flow Theory vs. Electron Flow Theory
  • Conventional flow theory (historical): Assumed positive charge movement from positive to negative.
  • Electron flow theory (modern): Electrons move from negative to positive because electrons are negatively charged.
  • In schematics, knowing high to low potential (source to neutral/ground) is crucial, regardless of flow theory.

Voltage, Current, and Resistance

• Voltage (Volts)
  • The force moving electrons, measured in volts (V).
  • A rating indicates the force moving electron, similar to pressure in a hydraulic system.
  • Analogous to the pressure in a garden hose.
  • Low voltage (e.g., 1.5V AA battery) is generally safe; high voltage is dangerous.
• Current (Amperes)
  • The rate of electron flow, measured in amperes (amps).
  • One amp equals 6.24 \times 10^{18} electrons flowing per second.
  • Can be liken to, the amount of water flowing in a garden hose, or cars on a highway moving from point A to point B
• Resistance (Ohms)
  • Opposition to current flow, measured in ohms (Ω).
  • Ω symbol is used as the Ohm's symbol.
  • Analogous to a sprayer resisting water flow in a garden hose or a choke point in traffic.
  • Generates heat (electrical friction); resistors can be designed to dissipate heat (e.g., space heater).

Ohm's Law and Watt's Law

• V = I * R (Voltage = Current x Resistance)
• I = V / R (Current = Voltage / Resistance)
• R = V / I (Resistance = Voltage / Current)
• P = I * V (Power = Current x Voltage), where P is power in watts.
• Given two values, you can calculate the third.

Using Ohm's Law and Watt's Law for Troubleshooting

• Example: Space Heater
  • A 1000-watt space heater plugged into a 120V AC source.
  • Calculate expected current: I = \frac{P}{V} = \frac{1000}{120} \approx 8.3 \text{ amps}
  • Measure resistance (de-energized): R = \frac{V}{I} = \frac{120}{8.3} \approx 14.5 \text{ ohms}
  • If resistance is infinite (open), the heating element is likely bad.
  • If resistance is zero (short), the circuit breaker would trip.
• These laws can help determine expected values and troubleshoot issues.

AC vs. DC

• Direct Current (DC)
  • Current flows in one direction.
  • Example sources: Batteries, photovoltaics.
  • Has polarity (positive and negative).
  • Used in laptops, phones, small electronics, LEDs, thermocouples, and PCBs.
  • Voltage and current are constant over time.
• Alternating Current (AC)
  • Current direction reverses periodically (cycles).
  • Generated by rotating equipment (generators) via a spinning magnet.
  • The standard in wall outlets.
  • Voltage and current vary over time, represented as a sine wave.
  • Frequency of 60 Hz. f = 60Hz Meaning a a cycle is completed 60 times in 1 second.

Metering AC and DC Voltage

• Metering DC Voltage
  • Select DC voltage setting on the meter.
  • Connect meter leads to appropriate locations.
  • The meter reads the difference in potential between terminals.
• Metering AC Voltage
  • Select AC voltage setting on the meter.
  • Meters read AC voltage in RMS (root mean square) to provide a DC equivalent.
  • RMS is calculated as: V{RMS} = \frac{V{peak}}{\sqrt{2}}
  • For a 120V circuit, the peak voltage is approximately 170V, but RMS provides a stable reading.
• Measuring voltage (AC or DC) involves measuring the potential difference between high and low sources.
• When measuring voltage across a closed circuit breaker, the reading will be near zero millivolts due to the same potential. Opening the breaker will show the full potential difference.

Metering Current

• Clamp meters are easier and safer than traditional multimeters: These measure the magnetic field induced around the conductor.
• Traditional multimeters require putting the meter in series, which involves opening the circuit (potentially unsafe).
• AC/DC clamp meter types
  • Fluke Wireless Clamp. Can connect to Bluetooth and a Fluke App