Cables volt drop

LV cable volt-drop when running at full-load 2.5% to 5.0%. 

Appendix G gives detailed calculations of cable volt-drops for the starting and full-load running conditions of a 500 kW induction motor that is to be started direct-on-line in a power system that is fed by three 3125 kVA generators. This appendix demonstrates the following aspects of starting large motors -... 

Note See Chapter 9 for a similar expression used with cable volt-drop). 

The nsual limit to volt-drop in three-phase cables feeding static loads is 2.5% at full load. 

Volt-drop developed across the cable under steady state and transient conditions. 

The secondary cable runs on its own cable rack to a switchboard. Both cable routes are short enough to neglect volt-drop considerations. Find suitable Cu/XLPE/PVC/SWA/PVC cable conductor sizes. 

The volt-drop in the left-hand side of the cable is Vsc,... 

When calculating the volt-drop in low voltage motor feeder cables it is necessary to consider three factors in particular -... 

Typical limiting values for the steady state volt-drop at the receiving end of LV and HV cables are -... 

Find the smallest cable size and its maximum route length to satisfy a running volt-drop of 5% and a starting volt-drop of 15%. Choose an XLPE insulated 600/1000 V 3-core cable to be routed in air. The ambient air temperature is 25°C. 

Since the cable volt-drop is significant it is necessary to revise the starting time duration and current from the data given by the manufacturer of the motor. 

Table 9.33 shows the volt-drop resnlts for all the available cables,... 

Table 9.33. Volt-drop in worked example the motor feeder cable for the ...

Cable cross-sectional area should be at least 50 mm, to comply with volt-drop. 

For cables having long route lengths the associated volt-drop may cause the margin in cnrrent capacity to be reasonably high, especially with low voltage feeders. 

These harmonics will cause two secondary problems. Firstly, the harmonic currents will flow in cables, transformers and generator windings and in so doing will immediately produce harmonic volt-drops in these series circuits. This in turn will cause the voltages at various points in the system to contain harmonic components, e.g. either side of a transformer, at motor control centres and... 

The near-rectangular line currents will produce volt-drops in the series resistance-reactance cables, overhead lines and transformers. These volt-drops will be non-sinusoidal and will distort the waveform at their intermediate points of connection. At snch points there may be a switchboard or distribntion board and the loads connected to them will experience the distorted voltage waveform. 

Now test for volt drop from Table 3.5 the volt drop per ampere per metre for a 10mm cable is 4.4mV. So the volt drop for this cable length and load is equal to ... 

Regulation 525 states that the drop in voltage from the supply terminals to the fixed current-using equipment must not exceed 3% for lighting circuits and 5% for other uses of the mains voltage. That is a maximum of 6.9V for lighting and 11.5V for other uses on a 230V installation. The volt drop for a particular cable may be found from ... 

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