In electrostatic precipitators, how do you make a positively charged wire?

all you need is high voltage power supply which is a circuit that electrons circulate through it.these equipments are capable of producing more than 30kv(low amper) between its outputs. there are several types of these HV power suppies some work with flyback transformers some uses some physical principals such as tesla coil. better check this out ramsey ion wind generator its function is nearly the same.