http://www.pln.co.id/statics/uploads/2017/06/Permen-ESDM-No.-28-Tahun-2016.pdf
Basically 0-200KVA = LV, 200 - 30,000KVA = MV and over 30,000KVA is HV. So, the contract load is 20MVA therefore it is an MV customer and as the transformers are 20KV the voltage is 20KV. HV in PLN's definition must be plus 20KV.