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Series Filters vs Parallel Connected Devices  
Among the Protective Devices (Surge Protection Device, or SPD) also called TVSS (Transient Voltage Surge Suppressor) there are two distinct types of configuration: Series Connection and Parallel Connection.
 

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1. Parallel Connected Devices
These devices include components such as SAD’s (Silicon Avalanche Diode) or MOV’s (Metal Oxide Varistor) being these the most used elements nowadays.
Fig. 1 shows the connection scheme.

 
 
Fig. 1
 
     
 
Fig. 2: Transient
 
Fig. 3: Cut achieved by MOV.
     
 
Fig. 4: Ringwave
 
Fig. 5 :No attenuation of Ringwave

Fig. 1 displays the typical application circuit of the parallel devices
Fig. 2 displays a set of transients that normally are present in the sine wave.
Fig. 3 the same transients as in Fig. 2, suppressed by the parallel connected device.
Figs. 4 & 5 recreate the before and after, respectively, the parallel connection (no variation).

The MOV’s can be used in high energy applications but with no critical load, due to this devices have a high residual tension. They are included in categories B & C, according to IEEE C6241.

 


2. Series Filters
These protective devices are series connected integrated with components, such as inductors and capacitors (L-C Circuit).
These types of devices are connected according to Fig. 6.

 
 
Fig. 6
 
     
 
Fig. 7: Transient
 
Fig. 8: Attenuation achieved by L-C Filters.
     
 
Fig. 9: Ringwave
 
Fig.10: Attenuation achieved by L-C Filters.


This type of circuit enables the effective attenuation, in a filter that is efficient in the diverse frequencies, that are components of the electrical noise (Ringwave) and the wave peaks caused by atmospheric discharges, but lack of high energy shunt elements.
They are included in the category A, according to IEEE C6241.


3. Parallel + Series Connected Devices
These devices combine both protection systems with a primary stage with MOV’s in parallel, and a series circuit, achieving a superior attenuation performance. These types of protectors take advantage of the great shunt capacity of the MOV’s and the high efficiency of the series connection. This are included in categories A, B & C, according to IEEE C6241.

Within the parallel + Series connected devices, we find the Active Filters, which hold the best performance in protecting the critical load. Some examples of application of these devices are as follows, remote telecommunications sites, electromedicine, industrial automation, robotics, aero-space industry, etc.



Active Filters with integrated primary and secondary stages
EC-Series devices with active filter are composed by two stages of protection, primary and secondary. The type of connection for these devices is series connection.
The first stage consists of shunting, whilst the second one involves active filtering, and it eliminates transients and disturbances both in Normal Mode (disturbances between phases or phase and neutral, also called Differential Mode) and in Common Mode (disturbances between phase and ground or neutral and ground).

“EC-Series” active filters will provide attenuation both for transients and disturbances, as well as constant noise  (low values of voltage in high frequency) that pollute the 50Hz or 60Hz sine wave, due to the increase in the loads that generate this effect on Energy lines.
Great or minimal disturbances are eliminated with the same efficiency.


It is well known that most electronic equipment do not receive current in sine waves, on the contrary, in general they tend to receive short current impulses. Active line filters “EC-Series” recognize this fact, and due to its very low impedance output, allow this non-linear current to be taken by the equipment without compromising the sine wave integrity (sine wave deformity).

The “Sine Wave Monitoring” allows spurious to be eliminated widely, with disregard of its point of creation within the sine wave.

 “EC-Series” active device constantly monitors the sine wave, when it detects a divertion different form its pre-set value (+/- 2V), it triggers itself taking a few nanoseconds to act. In the schematized figure we can appreciate the concept of “EC-Series”.
We appreciate a reference signal of 50Hz, obtained from a low pass filter Pi type. The distortion, instantly detected, activates the shunt element that reduces the disturbance reactance to the necessary level to neutralize the transient.

Simultaneously, the stored element restores Energy and fills the vacuum created by the phenomenon.
The parasite impulses, can appear in any point of the sine wave, and can be verified over and below the sine wave.

The over-impulse of the transient is absorbed by the usage of the series and shunt elements.
The fraction of the sub-impulse, on the other hand, responds to a current diminish and it is as destructive as overshoots.

The stored elements of the capacitive system of “EC-Series” filters, supply the energy lost in the negative hemicycle, recomposing the sine wave. This way, the protection against positive and negative impulses is equally effective in every point of the sine wave.

The graphics are an intellectual property of Energy Control SRL, and its reproduction or use is strictly forbidden.

 

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