Corporate Headquarters GPS Time Stamp AHC Corporate Network Station GHM 1 Firewall SCC: System Control Center RCC: Regional Control Center GMD DB: GMD Database AHC: Asset Health Center GHM: GIC/Harmonics Monitoring Station GHM 2 Station GHM n RCC n Station GHM 1 GMD DB SCC (Backup) Station GHM 1 SCC RCC 1 Station GHM 2 Station GHM 2 RCC 2 Station GHM n Station GHM n Secure Laptop Secure Remote Access Server Figure 3. GMD-an overview. provides standard outputs of either ac/dc current (e.g., 4-20 mA) or dc voltage (e.g., ±5 Vdc or ±10 Vdc). It is preferable to choose ±10-Vdc output to feed into a GIC relay. There are different design options available such as solid- or split-core. For a new transformer, it is desirable to choose the solid-core design. The split-core design can be used for a retrofit installation without outage requirements. The Hall-effect sensor can be chosen from different sizes based on the range of dc to be measured. Appropriate sensor size must be chosen to fit transformer neutral insulated cables. It is recommended that the dc sensor accommodate at least ±500-A dc current with 0.5% accuracy over an extended temperature range from -40 °C to +60 °C. Hall-effect transducers should be tested for accuracy. Additional tests such as environmental tests, measuring dc with an ac background, should also be performed to determine acceptance. GIc relay The GIC relay converts transducer analog output signals into numerical values. A transformer neutral lead may have a significant 60-Hz current (maybe as high as 100 A or more) due to system imbalance induced by untransposed lines, mismatched single-phase equipment, or unbalanced loading; hence, a built-in low-pass filter with cutoff frequency of 2-3 Hz is required to filter out the ac components. The GIC relay will pass GIC monitoring data via fiber to RTU or station computer in the control house (Figure 4) using distributed network protocol (DNP) 3.0 or International Electrotechnical Commission 61850 protocol over multimode fiber. DNP 3.0 protocol IEEE Elec trific ation Magazine / d ec em be r 2 0 1 5 25