Transient Waveforms

Agency Waveforms and Threat Levels

Performance standards have been developed over a 20+ year period by key agencies in order to 1) make recommendations relative to testing of TVSS equipment and 2) provide standards for comparison of claimed performance.

Three key waveforms are utilized as primary in the industry. Test waveform terms refer to rise-time (from 10% or 30% to 90% of crest rise time) and decay (50% of fall time from 10% or 30% of start of rise).

The most common waveform is the "Combination Wave" which has a voltage waveform of 1.2 m sec rise (30% to 90% of crest), 50 m sec duration (30% rise time to 50% decay) into an open circuit, and a current waveform of 8 m sec rise (10% to 90% of crest) and 20 m sec duration (10% of rise to 50% of decay) into a short circuit. This standard is referenced by ANSI 62.41, IEC 1000-4-5, UL 1449 2nd edition and CECC 42000. (See Figure 10)

Figure 10

The "Ring Wave" has a damped oscillation with a rise time (10% to 90% of crest) of 0.5 µsec and a frequency of 100 kHz. The decay factor is 0.6 during each half cycle. Figure 11 (Top) shows a ring wave (See ANSI Standard C62.41).

The "electrical fast transient" (EFT) represents transient bursts which occur during inductive load switching or relay contact bounce. The pulse is a burst of individual waveforms of 5 x 50 nsec for a 15 msec duration and repeated every 300 msec. Figure 11(Bottom) shows an Electrical Fast Transient/Burst train (Referenced in IEC 1000-4-4 1 1989).

Figure 11

Additional waveforms referenced on ANSI/IEEE C37.90.1-1989 are shown on Figures 12 and 13.

Figure 12

Figure 13

The set up for test utilizing these key waveforms is quite complex and expensive. Test equipment capable of forming the very specific high current voltage waveforms repeatedly is required along with great care in lead and probe set up. Specified test layout, use of filters and impedance devices and so on is critical and requires significant training.

The waveforms for the ANSI Standard are slightly different; also an oscillatory test wave (open circuit) is added.

Threat levels as defined by IEC are shown in Figure 14

IEC 1000-4-4 Electrical Fast Transient

Open-circuit output test voltage (+/- 10%)
Level	On power supply port, PE		On I/O (input/output) signal, data and control ports
Level	Voltage Peak kV	Repetition rate kHz	Voltage peak kV	Repetition rate kHz
1	0.5	5	0.25	5
2	1	5	0.5	5
3	2	5	1	5
4	4	2.5	2	5
x¹	Special	Special	Special	Special
1) "x" is an open level. The level has to be specified in the dedicated equipment specification.

The electrical fast transient (EFT) is a 5x50 nS waveform.

Level 1	Well shielded protected environment (e.g., computer room).

Level 2	Protected environment - separation of power and control cables from signal and communication cables (e.g., control room).

Level 3	Typical industrial environment (e.g., industrial process equipment, power plants).

Level 4	Severe industrial environment (e.g., outdoor industrial process equipment, power stations).

Figure 14

Threat levels as defined by ANSI/IEEE are shown in Figures 15a and 15b


A Outlets and Long Branch Circuits Outlets at more than 10 m (30ft) From category B All outlets of more than 20m (60ft) From Category C

B Feeders and Short branch Circuits Distribution Panel Devices Bus and Feeder Industrial Plants Heavy Appliance Outlets with "Short" Connections to Service Entrance Lighting Systems in Large Buildings

C Outside and Service Entrance Service Drop from Pole to Building Run Between Meter and Panel Overhead Line to Detached Building Underground Line to Well Pump

Figure 15a

IEEE Location Category Test Values

Location Category*	System Exposure	Voltage (kV)	Current (kA)	Effective Impedance (Ohms)
A1	Low	2	0.07	30
A2	Medium	4	0.13	30
A3	High	6	0.2	30

B1	Low	2	0.17	12
B2	Medium	4	0.33	12
B3	High	6	0.5	12

Standard 0.5 us-100 kHz Ring Wave

Location Category	System Exposure	Voltage (kV)	Current (kA)	Effective Impedance (Ohms)
B1	Low	2	1	2
B2	Medium	4	2	2
B3	High	6	3	2

C1	Low	6	3	2
C2	Medium	10	5	2
C3	HIgh	20	10	2

Standard 1.2 x 15 microsecond - 8 x 20 microsecond combination wave.

Figure 15b

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