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ASM

ASM surge arresters are intended for protection of power engineering a.c. devices against destructive operation of lighting and switching overvoltages.

Technical data

Item
rated voltage	kV_sk
continuous operating voltage	kV_sk
residual voltage at nominal discharge current U not higher than	kV_max
residual voltage at steep current impulse	kV_max
residual voltage at switching impulse 500A	kV_max
minimum creepage distance L (version with normal creepage distance)	mm
height	mm

Item		ASM 04	ASM 05	ASM 06	ASM 07	ASM 08	ASM 09	ASM 10	ASM 11	ASM 12	ASM 13	ASM 14	ASM 15	ASM 16	ASM 17	ASM 18	ASM 19	ASM 20	ASM 21	ASM 22	ASM 23	ASM 24	ASM 25	ASM 26	ASM 27	ASM 28	ASM 29	ASM 30	ASM 33	ASM 36
rated voltage	kV_sk	5,0	6,3	7,5	8,8	10,0	11,3	12,5	13,8	15,0	16,3	17,5	18,8	20,0	21,3	22,5	23,8	25,0	26,3	27,5	28,8	30,0	31,3	32,5	33,8	35,0	36,3	37,5	41,3	45,0
continuous operating voltage	kV_sk	4,0	5,0	6,0	7,0	8,0	9,0	10,0	11,0	12,0	13,0	14,0	15,0	16,0	17,0	18,0	19,0	20,0	21,0	22,0	23,0	24,0	25,0	26,0	27,0	28,0	29,0	30,0	33,0	36,0
residual voltage at nominal discharge current U not higher than	kV_max	14,0	17,5	21,0	24,5	28,0	31,5	35,0	38,5	42,0	45,5	49,0	52,5	56,0	59,5	63,0	66,5	70,0	73,5	77,0	80,5	84,0	87,5	91,0	94,5	98,0	101,5	105,0	115,5	126,0
residual voltage at steep current impulse	kV_max	14,5	18,3	21,8	25,5	29,0	32,8	36,3	40,0	43,5	47,3	50,8	54,5	58,8	61,8	65,3	69,0	72,5	76,3	79,8	83,5	87,0	90,8	94,3	98,0	101,5	105,3	108,8	119,8	130,5
residual voltage at switching impulse 500A	kV_max	10,0	12,6	15,0	17,6	20,0	22,6	25,0	27,6	30,0	32,6	35,0	37,6	40,0	42,6	45,0	47,6	50,0	52,6	55,0	57,6	60,0	62,6	65,0	67,6	70,0	72,6	75,0	82,6	90,0
minimum creepage distance L (version with normal creepage distance)	mm	250	250	250	370	370	370	370	370	370	490	490	490	490	490	490	610	610	610	610	610	610	730	730	730	730	730	730	850	850
height	mm	136	136	136	186	186	186	186	186	186	236	236	236	236	236	236	286	286	286	286	286	286	336	336	336	336	336	336	386	386

The principle of operation is the following: active current of order of microamps flows through an arrester at operating voltage. Each rise of voltage on overhead line, therefore on the terminals of a surge arrester causes prompt rise of current. Conductivity of varistors increases according to their voltage-current characteristic and the overvoltage is carried away to the ground by the surge arrester.
The drop of voltage in surge arresters called residual voltage does not exceed the withstand value of protected insulation, in the case of proper selection of surge arrester to the operating conditions. Return to operating voltage completes the operation of surge arrester which comes to standby position waiting for the next overvoltage and the heat is carried out to the environment.

Operation of a surge arrester does not cause any interference in the operation of systems. Short-circuit current which can flow through varistors in case of their damage does not cause sudden and dangerous to environment tear of housing, like in the case of porcelain housed surge arresters and it does not require suitable overpressure protection.

Construction

Basic part of surge arrester is the pile of varistors made of zinc oxide with other metal oxide additives. Varistors made by ceramic technology have high non linear voltage-current characteristic, high current withstand and stability of electrical parameters under continuous operating voltage during whole lifetime.
The pile of varistors is located in insulating material which is an internal housing of surge arrester and it provides very good mechanical strength. There are aluminium electrodes on both sides. An electrical contact between varistors and electrodes is obtained by suitable pressure. External housing of an arrester - integral and uniform - is made of silicone type LSR, which has very good insulating properties.
Design of a mould for direct injection of silicone type LSR provides the removal of air bubbles from the inside of surge arrester. It is confirmed by one of the routine tests - partial discharges measurement.
Advantages of silicone type LSR are the following:

flexibility even at low temperatures
high mechanical strength
resistance to atmospheric impact (e.g. ozone),UV radiation and heat
very good hydrophobic properties (see next to)
high resistance to ageing
less weight comparing to porcelain housed surge arresters

Silicone is the only material for housing that can transfer hydrophobic
properties (i.e. non-wettability) on surface layer of impurities. It causes decrease of leakage current and the danger of spark-over. Silicone is known as a self-cleaning material.
ASM surge arresters have got integral and uniform housing without any sheds pulled over a core. It is sure that impurities don't concentrate on a surface of housing and particularly on the contact between core and shed.

Operating conditions

ASM surge arresters are intended for operation at outdoor and indoor conditions (in moderate climate) at the temperatures from - 55°C (218K) up to + 55°C (328K), at altitude up to 1000 m above sea level. The power frequency of the system should not be lower than 48 Hz and higher than 62 Hz. The r.m.s. value of alternating voltage applied to the terminals should not exceed its continuous operating voltage Uc.
However, the r.m.s. value of alternating - current component of short circuit current in place of installation of a surge arrester should not be higher than 31,5 kA.