Voltage Drop in Moving Cable Systems

The choice of conductor size is frequently influenced by consideration of the voltage drop in the circuit.Economic factors dictate that a cable having the smallest conductor

size be chosen for any installation.However,care must betaken to ensure that the use of a cable having small conductors not result in such a large voltage drop from the power supply to the utilization equipment that the equipment not function properly.

It is common in moving cable systems for the cable to join a power supply to a motor.Assuming that the motor is designed to operate at the nominal supply voltage,voltage drops larger than 5% can result in decreased motor life.

Voltage drop can be calculated using the following equations.

For single-phase circuits,

Voltage drop,

V_d = Vs - Vr = (2×L×I×R)/1000

For three-phase circuits,

Voltage drop between conductors,

V_d = Vs - Vr = (√3×L×I×R)/1000

where Vs = voltage at the supply end

Vr = voltage at the receiving end

L = cable length (feet)

I = current (amps)

R = conductor resistance (ohms/1000 ft)

The conductor resistance used in these equations should be the resistance at the cable’s operating temperature.Industry standards normally provide resistance values at some reference temperature such as 20°C or 25°C.These values can be converted to resistance at the operating temperature by the use of the following equation.

Resistance at operating temperature,

Ro = Rr [1+0.00393(To -Tr )]

Where Rr = resistance at reference temperature

To = operating temperature (°C)

Tr = reference temperature (°C)

导体截面积的选择常常受到电路中电压降因素的影響。经济因素决定了在任何安装中都应选用具有最小导体截面积的电缆。然而，必须注意确保使用小截面积导体的电缆不会导致从电源到用电设备之间的电压降过大，从而使设备无法正常工作。

在移动电缆系统中，电缆将电源连接到电动机是常见的情况。假设电动机设计在标称电源电压下运行，那么大于5%的电压降可能导致电动机寿命缩短。

电压降可使用以下公式计算。

对于单相电路，电压降，

Vd = Vs - Vr = (2×L×I×R)/1000

对于三相电路，

导体间的电压降，

Vd = Vs - Vr = (√3×L×I×R)/1000

其中：

Vs = 电源端电压

Vr = 受电端电压

L = 电缆长度（英尺）

I = 电流（安培）

R = 导体电阻（欧姆/1000英尺）

这些公式中使用的导体电阻应为电缆在工作温度下的电阻。行业标准通常提供在某一参考温度（如20°C或25°C）下的电阻值。这些值可通过以下公式换算为工作温度下的电阻。

工作温度下的电阻，

Ro = Rr [1+0.00393(To -Tr )]

其中：

Rr = 参考温度下的电阻

To = 工作温度（°C）

Tr = 参考温度（°C）

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