Varistors; Sma Grid Guard; All-Pole Sensitive Residual-Current Monitoring Unit - SMA 9000TL Installation Manual

4 Product Description SMA Solar Technology AG
4.9

Varistors

Varistors are voltage-dependent resistors that protect the inverter against overvoltage. The inverter is
equipped with thermally monitored varistors.
Varistors can become worn and lose their protective function with age or repeated strain as a result
of overvoltage. The inverter detects if one of the varistors is defective and indicates an error
(see section 10 "Troubleshooting", page 56).
The varistors are specially manufactured for use in the inverter and are not commercially available.
You must order new varistors directly from SMA Solar Technology AG.

4.10 SMA Grid Guard

SMA Grid Guard acts as an automatic disconnection device between a grid-parallel generator
(e.g. a PV plant or small wind turbine system) and the electricity grid.
SMA Grid Guard is also a grid monitoring concept which detects errors by permanently monitoring
grid impedance, mains voltage and mains frequency. For example, SMA Grid Guard detects when a
stand-alone grid is formed and disconnects the inverter from the electricity grid immediately.
In some countries, the connection conditions require a device which protects grid-relevant operating
parameters against unpermitted changes. SMA Grid Guard performs this function.
Some country data sets are automatically protected after the first ten feed-in hours. The protected
country data sets can only be changed via a communication product on entry of a personal access
code, the SMA Grid Guard code, after ten feed-in hours (for information on changing parameters,
see the manual for the communication product). You will receive the SMA Grid Guard code from
SMA Solar Technology AG (to apply for the SMA Grid Guard code, see the certificate
"Application for SMA Grid Guard Code" at www.SMA-Solar.com).

4.11 All-Pole Sensitive Residual-Current Monitoring Unit

The inverter is equipped with an all-pole sensitive residual-current monitoring unit with an integrated
differential current sensor.
The all-pole-sensitive residual-current monitoring unit detects alternating and direct differential
currents. The integrated differential current sensor detects the current difference between the neutral
conductor and the number of line conductors for single-phase and three-phase inverters. If the current
difference increases suddenly, the inverter disconnects from the electricity grid.
If an external residual-current device is required or planned, you must install a residual-current device
which trips at a residual current of 100 mA or higher. That ensures that the inverter does not
disconnect from the electricity grid due to leakage currents caused by operation. If the locally
applicable installation regulations require the use of a residual-current device that trips at a lower
residual current, e.g. 30 mA, leakage currents caused by operation can cause false tripping.
24 SMC9-11TLRP-IA-en-51 Installation Manual