Application Note CCC-00-002 November 14, 2003

Series vs. Parallel Connected Transient Protection Steven P. Zwierlein, Sr. Applications Engineer

Control Concepts Corporation

Parallel connected Sine Wave Tracking (SWT) surge suppressors and series connected Active Tracking filters (ATF) both have their place in the Total Copper Wire Protection scheme. In order to achieve the most effective applications, it is important to first look at how both types of systems are connected to the facilitys power grid. Figure 1 shows connection diagrams for both types of systems. The parallel connected device is tapped off the load side of a service panel. Typically, a dedicated circuit breaker in the service or branch panel is used as the means of connection. On the other hand, the series connected filter, also wired to the load side of the service panel, is directly connected in-line with the protected equipment (typically hard wired with no quick means of disconnect). To understand why one type might be the better choice, for a particular application, it is necessary to now look at each from a component level.

.

Parallel Connected Devices: Parallel surge protective devices (SPDs)

generally contain components that clamp and divert transients away from the load. The technologies most commonly used are gas tubes, silicon avalanche diodes (SADs) and metal oxide varistors (MOVs). In this paper, MOVs are going to be the primary component discussed. MOVs are voltage sensitive components that begin to conduct current when a transient voltage condition exists on the line.

The diagram, in figure 2, shows the inside of a typical parallel surge protection device. The MOVs are attached across, or in parallel to, the incoming wiring from the panel. The length of the surge paths a, b, and c are dependent on the distance between the SPD and the panel it is connected to. This distance has a direct effect on the performance of the device. The greater the distance, the greater the amount of let-through voltage the loads are going to experience. Because parallel SPDs perform in this manner, installation rules require the SPD to be mounted as close as possible to the panel that it is protecting (general rule of thumb is less than five feet away). Often, this can be a difficult task for a contractor. Additionally, even if the contractor mounts the SPD as close as possible to the connecting panel, the lead length may have adverse effects on the desired performance.

's

N

G

ServicePanel Filter

TrackingActive "Protected"

Panel or

To

Loads

Series Connected Filter

Parallel Connected SPD

's

G

N

SPD

PanelService

To"Protected"

LoadsPanel or

Figure 1. Connection Diagrams

Figure 2.

Parallel-Connected Components

Application Note CCC-00-002 November 14, 2003 Series Connected Filters:

Active Tracking Filters (ATF) were originally designed to protect sensitive equipment from high-frequency noise. C w offers these products with para mponents that provide high-energfiltering.

Control Ccircuit to eliminateor L-C filters are thfor transient reductcapacitor and resiswhich means thateach phase and handle the maximuinductors together form a circuit capaof noise.

The ATFscomponents are previous section. mounted directly alead length (Figurare as short a posurge to get to the of let-though voltperformance.

The compothe following functithe diagram, the ssmooth current. shunt and absorbsparallel MOVs clamG) and normal combination of stagclamping voltage ra

Series-Co

Sine Wave Tracking: Sine wave tracking is an industry wide term

that refers to a device that contains parallel connected components as their sole means of transient protection. The majority of these products are parallel connected to the service or distribution

ontrol Concepts nollel and series co

y transient protection as well as

oncepts ATFs use a low-pass high-frequency noise. Low-pass e most popular type of circuit used ion and consist of series inductors, tors. ATFs are load dependent,

the series inductors located on neutral conductor, are sized to m current draw on the line. These with the capacitors and resistors

ble of absorbing a large bandwidth

parallel, high-energy, clamping similar to that discussed in the Surge components (MOVs) are cross the lines with no additional e 3). The a, b and c surge paths ssible allowing virtually all of the MOV. This minimizes the amount age and maximizes the circuit

nents shown in figure 3 perform ons. Starting from the left side of eries inductors block voltage and Next, capacitor/resistor networks normal mode noise. Finally, the p high-energy common mode (L-mode (L-N) transients. This ed components offers the tightest tings in the industry.

Figure 3. nnected Components Figure 4.

Sine Wave Tracking Performance

panel. A sine wave tracking device has a threshold at which it clamps high-energy spikes (figure 5). This threshold, which is commonly called the units clamping voltage, is based on three criteria:

1. The nominal system voltage 2. The size of the pulse 3. The length of leads

For example, a 120V parallel device that is subjected to 6kV, .5A pulse at 6 inches outside the case will typically have a clamping voltage of 400 to 600V. Additional benefits of parallel connected SPDs are as follows: 1. Usually lower price than series connected SPDs. 2. Because they contain no series components they

generally have smaller overall size. 3. Easy installation, power to equipment does not

need to be interrupted for servicing. Disadvantages of parallel connected SPDs include: 1. Performance is at the mercy of the installer,

because clamping voltage is dependent on lead length.

2. Let-through voltage at 0 point is significantly more than at 90 on sine wave.

3. High frequency noise may not be attenuated by the SPD, thus leaving sensitive equipment unprotected.

Application Note CCC-00-002 November 14, 2003 Active Tracking Filters:

Active Tracking is a Control Concepts patented term describing devices that contain series components. The devices are connected in series with the critical industrial loads they are protecting. Active tracking filters have the ability to attenuate high and low level transients at any point on the sine wave. This is accomplished by the addition of an L-C circuit to the existing parallel components. Figure 5 shows how high-energy transients and high-frequency noise are converted once they pass through the filter and to your sensitive equipment. Additional benefits of series connected Active Tracking Filters: 1. Converts potentially damaging high frequency

noise into clean reliable ac power. 2. Lowest possible clamping voltage because

modules are directly across lines. 3. Performance of device does not depend on

installer. Disadvantages of series connected Active Tracking Filters: 1. Load dependent therefore may be substantially

higher in cost than parallel connected devices. 2. Power to equipment must be cut for installation

and servicing.

Parallel (SWT) vs. Series (ATF): A major difference between a parallel connected Sine Wave Tracking device and a series connected Active Tracking Filter is the way they respond to high frequency noise. High frequency (also known as EMI/RFI) noise typically falls within the range of 10kHz to 150MHz. Figures 6 and 7 are EMI/RFI sweeps of a parallel and series connected devices. The X-axis of each graph indicates the frequencies injected into the device. The Y-axis represents the amount of attenuation, input versus output, measured in decibels. The higher the dB value, the better the filter. The plot in figure 6 show a narrow curve or notch of 80dB maximum at the approximately 1MHz. As one can see, the parallel connected device is providing very limited protection at frequencies other than 1MHz. On the other hand, the plot in figure 7 shows a deep bath tub shaped curve reaching 90dB attenuation over a wide range of frequencies. Comparison of the two graphs clearly shows that the ATF design provides much more protection from high frequency noise then the SWT.

Figure 6. EMI/RFI Sweep

Parallel Connected

Figure 5.

Active Tracking Filter Performance

Figure 7. EMI/RFI Sweep

Series Connected

Application Note CCC-00-002 November 14, 2003 Conclusion:

After reading this paper the following questions regarding transient protection should be able to be answered.

1. How are series and parallel devices

connected within a facility? 2. What types of components are used in a

parallel TVSS? 3. What type of components are used in a

series filter? 4. What protection does a TVSS provide? 5. What protection does a ATF provide? 6. What is the major difference in protection

between a TVSS and ATF?

During the procurement process the decision will need to be made between purchasing a series filter or parallel SPD. Answering this final question should make this decision easier. Are you trying to protect against the distruction of equipment, the disruption of machines or both?

If protection of equipment against destructive high-energy transients is required, then a parallel connected device is likely to be the most logical solution. On the other hand, if sensitive equipment is being disrupted by high frequency noise, then a series connected filter may be the right choice. Sometimes power quality equipment is installed before any problems arise, and it is not known what types of problems exist. In this case the staged approach is suggested, where both parallel and series connected devices are used within the facility. References: Cole, B. (May, 1994) Theoretical Analysis of an L-C, Low-Pass Filter. Control Concepts Corporation, Binghamton, NY Control Concepts. (1999) Industrial Strength Protection Catalog Binghamton, NY :Author.

Series vs. Parallel Connected Transient ProtectionSteven P. Zwierlein, Sr. Applications EngineerParallel connected Sine Wave Tracking \.Active Tracking Filters (ATF) were originally designed to Control Concepts ATFs use a low-pass circuit to eliminate hiThe components shown in figure 3 perform the following functSine Wave Tracking: