Measurements of transient electrical noise on low voltage distribution systems

Electrical noise measurements which were undertaken in preparation of designing a low-frequency (below 100 kHz) carrier current system for use in protective relaying are discussed. Steady-state measurements were made to assess the fluctuating noise level on a 600 V bus over a 24 hour period, and transient measurements were taken to discover the extent of the electrical noise generated in the few cycles following the initiation of an arcing fault. The steady-state measurements reveal only a small amount of noise, but show the importance of considering the effects of noise-generating loads in the design of any carrier current system. Transient measurements reveal a tremendous amount of electrical noise, especially at low frequencies. However, because this noise is still relatively small for frequencies above 50 kHz, there would be little difficulty operating a carrier system during transient electrical disturbances.<>