Standards for symbols

Symbols of Electrical Things
Standards for symbols
An electronic symbol is a pictograph used to represent various electrical and electronic devices (such as wires,batteries, resistors, and transistors) in a schematic diagram of an electrical or electronic circuit. These symbols can (because of remaining traditions) vary from country to country, but are today to a large extent internationally standardized. Some symbols represent components which ceased to be used routinely as newer technologies were introduced (such as vacuum tubes)


Standards for symbols

Contents

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• 1 Standards for symbols
• 2 Reference designations
• 3 Gallery of common electronic symbols
  • 3.1 Resistors
  • 3.2 Capacitors
  • 3.3 Transistors
  • 3.4 Diodes
  • 3.5 Vacuum tubes
  • 3.6 Switches
  • 3.7 Miscellaneous
• 4 See also
• 5 References
• 6 External links

Symbols of Electrical Things.

Miscellaneous.

Symbols of Electrical Things.

An electronic symbol is a pictograph used to represent various electrical and electronic devices (such as wires,batteries, resistors, and transistors) in a schematic diagram of an electrical or electronic circuit. These symbols can (because of remaining traditions) vary from country to country, but are today to a large extent internationally standardized. Some symbols represent components which ceased to be used routinely as newer technologies were introduced (such as vacuum tubes).

             
        

Definitions Of Electrical Energy

Definitions Of Electrical Energy

1   Electricity: energy made available by the flow of electric charge through a 


conductor; "they built a car that runs on electric 


2    Electric potential energy, or electrostatic potential energy, is a potential energy 


associated with the conservative Coulomb forces within a defined system of point 


charges. The term "electrostatic potential energy" is preferred here because it seems 


less likely to be misunderstood.


3   The energy associated with electric charges and their movements.


4    The generation or use of electric power measured in kilowatt-hours, megawatt-


hours or gigawatt-hours


5       The quantity of electricity delivered over a period of time. The commonly used 


unit of electrical energy is the kilowatt-hour (kWh).

Power Factor "cosφ".

Power Factor

It is common to define the Power Factor - PF - as the cosine of the phase angle between voltage and current - or the "cosφ".

 The power factor defined by IEEE and IEC is the ratio between the applied active (true) power - and theapparent power, and can in general be expressed as:

PF = P / S         (1)

where

PF = power factor

P = active (true or real) power (Watts)

S = apparent power (VA, volts amps)

A low power factor is the result of inductive loads such as transformers and electric motors. Unlike resistive loads creating heat by consuming kilowatts, inductive loads require a current flow to create magnetic fields to produce the desired work.

Power factor is an important measurement in electrical AC systems because

• an overall power factor less than 1 indicates that the electricity supplier need to provide more generating capacity than actually required
• the current waveform distortion that contributes to reduced power factor is caused by voltage waveform distortion and overheating in the neutral cables of three-phase systems

International standards such as IEC 61000-3-2 have been established to control current waveform distortion by introducing limits for the amplitude of current harmonics.

Example - Power Factor

A industrial plant draws 200 A at 400 V and the supply transformer and backup UPS is rated 200 A × 400 V = 80 kVA.

If the power factor - PF - of the loads is only 0.7 - only

80 kVA × 0.7

    = 56 kW

of real power is consumed by the system. If the power factor is close to 1 (purely resistive circuit) the supply system with transformers, cables, switchgear and UPS could be made considerably smaller.

Any power factor less than 1 means that the circuit's wiring has to carry more current than what would be necessary with zero reactance in the circuit to deliver the same amount of (true) power to the resistive load.

A low power factor is expensive and inefficient and some utility companies may charge additional fees when the power factor is less than 0.95. A low power factor will reduce the electrical system's distribution capacity by increasing the current flow and causing voltage drops.

"Leading" or "Lagging" Power Factors

Power factors are usually stated as "leading" or "lagging" to show the sign of the phase angle.

• With a purely resistive load current and voltage changes polarity in step and the power factor will be 1. Electrical energy flows in a single direction across the network in each cycle.
• Inductive loads - transformers, motors and wound coils - consumes reactive power with current waveform lagging the voltage.
• Capacitive loads - capacitor banks or buried cables - generates reactive power with current phase leading the voltage.

Inductive and capacitive loads stores energy in magnetic or electric fields in the devices during parts of the AC cycles. The energy is returned back to the power source during the rest of the cycles.

Power Factor for a Three-Phase Motor

The total power required by an inductive device as a motor or similar consists of

• Active (true or real)  power (measured in kilowatts, kW)
• Reactive power - the nonworking power caused by the magnetizing current, required to operate the device (measured in kilovars, kVAR)

The power factor for a three-phase electric motor can be expressed as:

PF = P / [(3)^1/2 U I]         (2)

where

PF = power factor

P = power applied (W, watts)

U = voltage (V)

I = current (A, amps)

Typical Motor Power Factors

Power (hp)	Speed (rpm)	Power Factor
		1/2 load	3/4 load	full load
0 - 5	1800	0.72	0.82	0.84
5 - 20	1800	0.74	0.84	0.86
20 - 100	1800	0.79	0.86	0.89
100 - 300	1800	0.81	0.88	0.91

• 1 hp = 745.7 W