ANSI/IEEE Device Numbers. Protective relays are commonly referred to by standard device numbers. For example, a time overcurrent relay is designated a 51 device, while an instantaneous overcurrent is a 50 device. Multifunction relays have combinations of device numbers. A 27/59 device, for example, is a combination under/over voltage relay.
At 0Â° Celsius the speed of sound in U.S. textbooks is 331.3 m/s. At 20Â° Celsius the speed of sound then is 343.21 m/s, rounded 343 m/s. At 0Â° Celsius, the speed of sound in German textbooks is 331.5 m/s. At 20Â° Celsius the speed of sound then is 343.42 m/s, rounded 343 m/s.
More commonly the term refers to the speed of sound in air. The speed varies depending on atmospheric conditions; the most important factor is the temperature. Here we have used standard sea level and a temperature of 15 C / 59 F, so the speed of sound (in air) is aprox: 340m/s, 1225 km/h, 761 mph, 661 knots. more info.